so going over all the pathfinder/3.x/D20 books, and there is very little to none summoning feats. So in an attempt to rectify this heres what i came up with. Any constructive feedback for balancing/requirements/etc is appreciated.
Augmented summoning
-Small Summoning: Summons one size smaller summons
-Tiny Summoning: *reqs Small summoning* Summons two size smaller summons
-Giant Summoning: Summons one size larger summons
-Huge Summoning: *reqs Giant summoning* Summons two sizes larger Summons
-Blazing Summoning: Summons gain fire subtype, +1d6 fire dmg
-Frozen Summoning: Summons gain cold subtype, +1d6 cold dmg
-Nimble Summoning: Summons gain +4 init, +10' speed
-Armored Summoning: Summons gain +4 natural armor
-Greatly Augmented Summoning: +6 str/con +4 dex
-Electrified Summoning: *reqs greatly augmented summoning* +1d6 electricity dmg
-Acidic Summoning: *reqs greatly augmented summoning* +1d6 Acid dmg
I'm surprised you had a hard time finding abilities related to summoning; there seems to be a prolific amount of pathfinder content in that regard. None of the other schools of magic seem to get the special treatment Conjuration gets. (Why don't Evokers, Diviners, Abjurers, Transmuters, Enchanters, Illusionists, and Necromancers get things as nice as Augment Summoning?)
Anyway, here's what you'll find in the rules.
Here are some Sorcerer bloodline arcana:
Abyssal Bloodline Arcana: Whenever you cast a spell of the summoning subschool, the creatures summoned gain DR/good equal to 1/2 your sorcerer level (minimum 1). This does not stack with any DR the creature might have.
Celestial Bloodline Arcana: Whenever you cast a spell of the summoning subschool, the creatures summoned gain DR/evil equal to 1/2 your sorcerer level (minimum 1). This does not stack with any DR the creature might have.
And some abilities: (Could be gained through Eldritch Heritage)
3rd level Groveborn Bloodline Ability:
Lush Summoning (Su): At 3rd level, whenever you summon creatures with a conjuration (summoning) spell, you can decide that they appear green and leafy. The natural armor bonus of such creatures is increased by +2, and they gain a +4 bonus on saves against paralysis, poison, polymorph, sleep, and stunning. This bloodline power replaces photosynthesis.
9th level Primal Bloodline Ability:
Elementalist Summoning (Su): At 9th level, whenever you summon a creature, it gains energy resistance 10 against the energy type that matches your elemental bloodline (if it already has such resistance, its resistance increases by +5), and its natural attacks deal an additional 1d6 points of damage of the same energy type. This bloodline power replaces elemental blast.
15th level Abyssal Bloodline Ability:
Added Summonings (Su): At 15th level, whenever you summon a creature with the demon subtype or the fiendish template using a summon monster spell, you summon one additional creature of the same kind.
Superior Summoning
You can summon more creatures.
Prerequisites: Augment Summoning, caster level 3rd.
Benefit: Each time you cast a summoning spell that conjures more than one creature, add one to the total number of creatures summoned.
Moonlight Summons
Your summoned minions are infused with the power of the moon.
Prerequisites: Spell Focus (conjuration), able to cast summon nature's ally.
Benefit: Creatures you summon shed light as a light spell. They are immune to confusion and sleep effects, and their natural weapons are treated as silver for the purposes of overcoming damage reduction.
Starlight Summons
Your summoned minions slink along under the shadows of the stars.
Prerequisites: Spell Focus (conjuration), able to cast summon nature's ally.
Benefit: Creatures you summon gain the Blind-Fight feat, a +5 bonus to Perception and Stealth checks in dim light or darkness, and their natural weapons are treated as cold iron for overcoming damage reduction.
Sunlight Summons
Your summoned minions shine with the power of the sun.
Prerequisites: Spell Focus (conjuration), able to cast summon nature's ally.
Benefit: Creatures that you summon shed light as a light spell. They are immune to blinding or dazzling effects, and their natural weapons are treated as magical for overcoming damage reduction.
Sacred Summons
The minions of your divine patrons stand ready to answer your call.
Prerequisites: Aura class feature, ability to cast summon monster.
Benefit: When using summon monster to summon creatures whose alignment subtype or subtypes exactly match your aura, you may cast the spell as a standard action instead of with a casting time of 1 round.
Skeleton Summoner
The walking dead respond to your call.
Prerequisites: Spell Focus (necromancy), ability to cast summon monster.
Benefit: Add “human skeleton” to the list of creatures you can summon with summon monster I and “human skeletal champion” to the list of creatures you can summon with summon monster III.
Once per day, when you cast summon monster, you may summon a skeletal version of one of the creatures on that spell's summoning list (apply the skeleton template to that creature to create this monster).
Fire Music
Your ability to command fire and bardic music has created a strange blend of both magics.
Prerequisites: Spellcraft 5 ranks, ability to cast bard spells, ability to cast an arcane fire spell from some other spellcasting class.
Benefit: When you cast a bard spell that deals damage, you may replace the spell's normal damage with fire damage or split the spell's damage so that half of it is the normal damage type and half is fire damage.
If you cast a summon monster spell as a bard spell, you may choose to give the summoned creature a fiery appearance, which gives it fire resistance 5 and adds +1 fire damage to all of its natural attacks. The creature sheds dim light in a 5-foot radius. This aspect of the feat has no effect if the creature already has the fire subtype.
When you use this feat, the affected spell gains the fire descriptor.
As for your homebrew feats, here are my suggestions:
This should replace the first 4 feats you made:
Sizing Summons
If summoning a monster would take 1 round, you may spend a move action during the turn the monster would be summoned to use this feat.
If summoning a monster would take a standard action, you may instead spend a full-round action to use this feat.Each creature you conjure with any summon spell while using this feat will have its size category increased or decreased by 1 for the duration of the spell that summoned it. The bonuses and penalties gained are like Enlarge Person and Reduce Person.
A summoned creature cannot be made fine or colossal by this feat.
...not so sure about changing 2 size categories. I'd say just skip that.
These could replace Blazing, Frozen, Electrified, Acidic:
Elemental Summons
Prereq: Spell Focus (Conj)
Whenever you conjure with any summon spell, you may choose Fire, Cold, Electric, or Acid;
If you chose fire, creatures summoned gain fire resistance 5 and deal an extra 1d4 fire damage on all natural attacks.
If you choose ice, creatures summoned gain cold resistance 5... So on and so forth.Advanced Elemental Summons
Prereq: Elemental Summons
Increase the resistance gained to 10 and the damage added to 1d6.
I'm not sure how reasonable it would be to, say, turn a tiger into the pure essence of fire or whatnot, so this seemed like a decent compromise.
As for the rest:
Nimble Summoning seems a little pointless; initiative doesn't do anything and summoned monsters already tend to have good movement speeds.
For Armored Summons... I'd say try to take a cue from the Lush Summoning ability; give +2 natural armor to your summons and add a boost on certain saving throws.
For Greater Augment Summoning, I'd leave it at just +6 str and +6 con. (increased from +4 str and +4 con) Augment Summoning is an amazing feat in its own right; sort of the hallmark for all people who consider themselves summoners. If you wish to further specialize in summoning, the power boost from there should be a bit more modest.
Making a creature one size category smaller or larger costs one spell level. 2 size categories costs 4 spell levels.
While you can summon 2 tiny instead of one M size, 2 huge instead of one M sized is a misuse of logic. Hopefully the author edited that out and this will make no sense.