Any effects that say that the Human can’t attack (such as that of Propaganda, or if you get a Human with defender) affect only the declaration of attackers. They won’t stop the Human you find from entering the battlefield attacking.

If more than one non-Human creature you control attacks, Winota’s ability triggers separately for each of them. For example, if three non-Human creatures attack, you won’t look at the top eighteen cards of your library at once; you’ll look at six, finish resolving the ability, and then repeat the process twice more as the other instances of the ability resolve.

Although the Human is an attacking creature, it was never declared as an attacking creature. This means that abilities that trigger whenever a creature attacks won’t trigger when it enters the battlefield attacking.

You choose which player or planeswalker the Human is attacking. It doesn’t have to be attacking the same player or planeswalker that the non-Human creature is attacking.