1. Dunno, but OT does
2. …..sure?
3. Ye, not mandatory
4. Ye, not mandatory

I can answer from Soepboi himself
Power attacks depend on your character.
Now in my words..
I’m sure there are several combos you can do just not OP
combos
Grab attacks arent mention in rules I think
I’ll let the admins decide that
Special moves depend on character
Let’s go to SSBU
Solid Snake is based on tactical.
So his ranged attack is rocket launcher.
I’m sure arcade fighters works like that
I haven’t focused on the group in a while so bare with me.

Most types of combo systems are fine, try in keep in mind the getting hit sprites of other characters though, stuff like Tekken type juggled animations might not be accommodated for in most sprite sheets.

No rule against it, but once again try to create “grabs” that don’t require too specific poses* (Like a headlock*) try making grab attacks that can use the sprites like grounded or knocked back. Or you could just make unblockable moves in their place.

Go right ahead, special moves are allowed.

Same with ultimates.

Grabs
Haven’t really optimized the engine to handle something like that, could work

Combo
Idk what you really mean by that, but stuff like “cancels” (do a specific attack then the next attack costs less frames = combo) and launches are a thing, if you’re talking about rekkas/natural combos (moves that have certain follow-up moves that cant be used normally), then yea that’s a thing

Ranged
It’s optional but if you really want to go for it

Ultimate
Again, optional, i’m currently working on it in the beta version for Tanner because he’s the only one with meter so far, but if you’d like then sure go ahead!