Ok, so then once I hit level 20, I want heroic reincarnation?
That will do everything I said above and keep your action points, plus get past life feat?
I can do this three times in the same class to max out?
Action points are earned 4 per level as you go through the levelling process, capping at 80 once you take level 20.
Doing a heroic reincarnation will put you back to level 1 character creation where you can redo race/class/appearance (not name & gender though) & you'll gain the past life benefit for that class. All your items will go into a reincarnation cache, which is a withdrawal-only portion of your character bank. Make sure not to have any summoned weapons (flame blade & shadowblade spells) in your inventory though, as there's a known bug that can cause issues later.
Yes, you can stack past life feats up to 3 times per class. Only 1 TR for each class is necessary to qualify for the completionist feat. Archetypes have their own past life feats with different benefits but they count as that base class to qualify for completionist.
Lesser reincarnation is basically a character rebuild so you can immediately re-level back to where you were before with the option to change feats & appearance. If your character is only a 28 point build they'll also be upgraded to 32 points in the process.