Down-B works exactly as it did before.
Side-B can still be done with Jump or Attack, but not with C-Stick unless you switch Smash to Attack.
Depends on the situation.
Uair, Fair, Nair are good enough anti-airs depending on their positioning. Utilt is more of a commitment and worse range so probably not. On the ground, Ftilt or just grab if in range. That's about it.
Never HA OoS though... No.
Well, that's why his approaches are bad.
If your approach options are "Try to make my opponent mess up" or "Rely on my opponent making a mistake" then guess what? Your approach is ****.
A good approach option would be approaches that your opponent is forced to respect... Things that put you in a positive situation. We don't really have anything that safe or reliable. Characters like Sheik have amazing approaches because she can just Fair your shield with no lag, safe spacing, and is in a positive situation every time on your shield unless she whiffs or messes up spacing. She hits your shield, you try to grab OoS and miss, she can punish with another Fair. If you stay in shield, she can land and grab you out of it. That is an incredibly ideal approach because it creates situations where she wins.
Sonic can
sort of do this, but his are based nearly completely off of reactions, so with proper conditioning, Sonic has the tools to effectively open up your opponent, but inherently, his approaches themselves are bad because they're not safe or frame advantageous. They're only seemingly good because they're kind of annoying and aren't as much of a commitment as some characters. At the end of the day though, the strongest thing about his approach is that it can be manipulate, but as a typical approach, they are bad.
You answered your own question.
"Spin to win" is garbage. If anyone is falling for it, then they're bad. End of story. Not your fault for abusing it on someone. Why stop doing it if it works?
Against any player with half a brain in the match-up would body you if you spin to win, because it simply does not work for a multitude of reasons.