Mythic Magic

[The Total Package]

Assuming I am level 14 and an Occult Sorcerer, how does this Feat work?

You convert your mythic power into a magical effect. When you gain this feat, choose up to three spells of 1st or 2nd rank that take no more than 3 actions to cast and that are either instantaneous or have a duration of 10 minutes or less. You can spend a Mythic Point to cast any of those spells for their normal action cost and use mythic proficiency to determine your spell attack rolls and spell DCs, and the spells are automatically heightened to a rank equal to half your level (rounded up). If you don’t normally have the ability to cast spells, you use Charisma as your spellcasting attribute modifier; otherwise, you use the spellcasting ability associated with your spellcasting class. You gain the Cast a Spell activity only for spells cast with this feat; you don’t otherwise gain the typical benefits of being a spellcaster.

Special At 14th level, add one spell of 3rd rank for you to cast using this ability. At 20th level, add one 4th-rank spell.

Can I choose any spells from any tradition?

[Tridus]

I don't see why not. You don't need to be a spellcaster at all to take this. It's got no prerequisites, no tradition limitations, and even gives you Cast a Spell for spells cast from this feat.

[Theaitetos]

Yes, you can take spells from any tradition.

So it's a good opportunity to "steal" some good spells from the other lists, and since it's auto-heightened it's also a good opportunity to take incapacitation spells – like Calm, Sleep, Paralyze, … – or spells with counteract checks (at mythic proficiency!) – like Dispel Magic, Cleanse Affliction, Clear Mind, ….

p.s.: RAW this feat would even allow you to take Focus spells like Earth's Bile, Sky Laughs at Waves, Trickster's Mirror, Untamed Shift, …

[The Total Package]

Wow, so I could get Calm, Floating Flame and Tremorsense (for second level optioms), and Paralyze for third level? And all would be heightened to 7th level in this example?

[Theaitetos]

Yes, exactly.

Though Tremorsense isn't really benefiting from mythic proficiency; there are also other ways to obtain special senses, e.g. a Saurian Spike.

Sustained spells are pretty good options, as they continue to benefit from the mythic proficiency, like the Floating Flame you mentioned, but also Illusory Creature (2 x 8d4 mental damage per Sustain) or Spiritual Armament (4d8 sanctified spirit damage per Sustain), as both use mythic attack rolls for the duration.