Currently, ASWM can run on any Spigot version from 1.18.2 up to 1.19.2. If you are running on an outdated version, use SWM.
Yes, you can! However, it does not work on versions 1.19+.
Go to Installing Slime World Manager and follow the steps described there.
I'm getting a javassist.CannotCompileException: [source error] acceptConnections() not found in net.minecraft.server.v1_14_R1.ServerConnection error on startup.
You are running an outdated spigot version. Please update to the latest version. If this keeps happening after updating, open an issue.
Multiverse-Core detects ASWM worlds as unloaded, as it cannot find the world directory, and then just ignores them. There should not be any issues; however, Multiverse-Core commands will not work with ASWM worlds.
The Slime Region Format can handle up a 46340x4630 chunk area. That's the maximum size that SWM can theoretically handle, given enough memory. However, having a world so big is not recommended at all.
There's not a specific value that you shouldn't exceed - except for the theoretical limit, of course. ASWM keeps a copy of all the chunks loaded in memory until the world is unloaded, so the more chunks you have, the bigger the ram usage is. How far you want to go depends on how much ram you are willing to let ASWM use. Moreover, the ram usage per chunk isn't a constant value, as it depends on the actual data stored in the chunk.