Getting better at melee can be easier than getting better at ranged when you're constrained on feats. However, you should probably know whether your DM will be enforcing the soft cover rules against reach weapons. If so that doesn't make them bad, but it would make them less than ideal for attacking from behind summoned monsters. Taking a -4 on attacks could be particularly troublesome when you're trying to use Power Attack.
I still don't see the appeal of Herald Caller over Evangelist unless you just want to be more flexible with your spell selection, but if the idea of calling heralds appeals to you more than that of preaching Erastil's virtues you should still do fine. Maybe it is just tough to trust that the summoned monsters can get things done for you, but Kingmaker is actually very well suited to a summoning focused caster, and a +3 bonus to hit and damage (or maybe more with BadBird's build) would be a big benefit for summoned monsters, the Magus, and the Skald. The usefulness of Inspire Courage is proportional to the number of attacks the party generates, and a party with summoned monsters can generate a lot.
Yep, that should work with mounting a flag on the longspear.
Sure, I guess that taking Flagbearer early is nice since it helps the Magus and Skald as well as you and your summons. I'd still aim for Augment Summoning longer term though. Maybe you could think about something like this?
Evangelist (Flag)
1st - Flagbearer, Combat Reflexes
3rd - Sacred Summons
5th - Boon Companion
7th - Spell Focus (Conjuration)
9th - Augment Summoning
11th - Discordant Voice (+1d6 sonic damage)
13th - Summon Good Monster (add Legion and Shield Archons to your list)
Another option due to the amount of downtime available in Kingmaker could be to take Craft Wondrous Items instead of Combat Reflexes (shuffling other feats around a bit). That could potentially cut the rather high cost of Banner of the Ancient Kings in half.
No way an Evangelist is a better summoning build than a Herald Caller!
The flexibility in spell selection with the Herald Caller could probably be pretty nice, but the Evangelist grants more combat bonuses. There are also other PCs in the party, not just summoned monsters, and those PCs might resent the summoned monsters less if the PCs get some buffs too.
Herald Caller can channel heals to his monsters from unlimited range at full strength (unlike Evangelist) and still has spontaneous heals/harms as well as spontaneous summons and only has to invest a bit in feats to become an even better summoner!
Regarding party (and monster) buffs... once you get 4th level casting, all you need is Blessing of Fervor!
The thing is, Evangelist, Flagbearer and a Banner of the Ancient Kings is a combined +5 to the attack and damage of all minions by the time it's affordable, which is a huge boost to minion power. Plus, all other allies including the Evangelist get it as well...
Ahhh yes..... but there is nothing stopping a Herald Caller getting the Flagbearer feat and a Banner of the Ancient Kings either and since its far less feat starved than the Evangelist in terms of a summoner build (the Evangelist has to invest in 2-3 feats to be good whereas the Herald Caller could invest nothing and still be very good), it becomes a more efficient choice.
Flagbearer and BAK is much more marginal on a character without Inspire Courage though; it caps at +2 morale, rather than being a +5-6 combined buff. The +3 from Inspire alone is more than the damage boost from Augment Summons, and you can still take Augment. You're quite right that the Herald Caller is the better summoner; it's just that the Evangelist is a great party buffer on top of being a good summoner, which translates to uniquely powerful summons (and more combat power for the summoner as well).
Inspire Courage is a pretty big deal, and healing summoned monsters sounds like a pretty dull job anyhow.
As nobody's brought it up thus far, I'm gonna suggest you look at the Evangelist PRC, as it might help your archer build considerably.
Biggest pros of it will be 9/10 progression in all cleric class features, +2 AC, +Wis to hit/damage with longbows, the ability to copy an animal companion, some spell-like abilities, and a pretty nifty customizable PRC capstone at level 16.
You'd give up only one effective cleric level for all that.
PRC here: http://www.d20pfsrd.com/classes/prestige-classes/other-paizo/e-h/evangelist
Erastil boons here: http://archivesofnethys.com/DeityDisplay.aspx?ItemName=Erastil
adding Dex+Wis to attacks and Str+Wis to damage on a longbow should be especially effective for a cleric, and doubling your animal companion (assuming you took animal domain) is never a bad thing.