Yes, you can do that (you can also pick one from Animal Power and three from WHMD, because Animal Power can also be converted into WHMD).
Yep.
Let's see,
lvl 1 and 2 would give 1 tentacle each (2 total)
lvl 1 feat for an extra tentacle (3 total)
lvl 3 and 4 I would use for Rage and probably size up to be practical (grapple bonus) but i could alternately max tentacles (3 large, 6 medium)
lvl 3 feat for 3 more tentacles (6 large, 9 medium)
lvl 5 and 6 both for size increases or extra tentacles (6 gargantuan, 21 medium)
lvl 6, 9, 12, 15, 18 feats for extra tentacles (36 gargantuan, 51 medium)
Maybe you could argue delaying your flaws until lvl 5 for 12 more tentacles, but we're already pretty scarily tentacled. I wonder which would be more effective damage-wise, 36 gargantuan or 51 medium. Assuming you're stacking strength like you should be, 15 extra secondary attacks sounds amazing. On the other hand, gargantuan would also increase the 'size' of the tentacle damage so... Maybe I'll sit down and theorycraft that later.
Also, made me think, would improved grab (from WHMD?) apply to all the tentacles or would it just give it to one actual attack? Either way, maybe a one-level dip into scaled horror would be better anyways. That's a TON of grapple checks, all of which would do a TON of damage... Once we're up to that many grapple checks, I'm thinking Spines would pay off... Maybe pounce as well?
