Basically, it’s hard to say until you try it. Imports are pretty weird, there’s no one-size-fits-all.
Expect to wipe the Discourse database a few times in case you don’t get it quite right. This is required if you make changes to the import script to move data that got missed, as already-imported records are skipped.
Pay special attention to data from plugins. Categories will definitely be transferred. User groups - probably not, but read the import script (if groups are important, you’ll want to add that to the script).
The default behavior is for everyone to need a password reset, but you can use this plugin (will probably require import script changes):