Heros are mortals you control (read play) directly. You say "Go slay X" and they go slay X. You say, "Be a dignitary to a foreign race and get them to agree to X." You say, (If they're magically inclined) "teach other mortals X spell" they do so. You say "Go steal X from X location" they go do it.
They're an additional piece, and are mostly used as a way to influence the world without spending IP or to do some things that it wouldn't make sense for a god to do. Basically you just use 5 IP to set up a particular mortal to do your bidding (and in return they become better and more relevant than the masses)
So your turn would go:
"My god does X"
"My hero does X"
The first species of slime is already mostly intelligent, it would probably only take 7 or so IP. The second ehhhh, 12ish? 12 sounds good. Most slimes are a bit dumber than animals, and so it would cost a little more to get them to sapience. The exception being the hydraslime, its strangely intelligent for a slime.
You're completely right there. Its most likely 10-15, depending on how easily the creature can achieve sentience from their current state.
Better Question: Price for Uplifting a PLANT to Sentience.
Uhhhhhhh. IP wise? They aren't too different from simple animals as far as cost is concerned. So a few more points than an animal, so like 10-18(ish). Really depends on the plants. We already have one and a half species of sapient plant floating around, so it shouldn't be too out there.