I think I read somewhere that someone said if you turn of tourists (allow tourists: false) you can’t invite sims from other worlds or something like that?

My sim hasn’t traveled yet so I can’t really try it out right now?

you can invite sims from foreign worlds even if you have tourism disabled in Register, this is not an issue. You can choose to do this either the EA way (where they may "decide" to not bother showing up) or by way of MC's Invite Over command (where they show up in town right away and begin making their way over to wherever the sim is who invited them).

However if you have Register set to a 100% chance of tourists leaving each cycle, don't expect your guests to be able to hang around for very long before they get strongly pushed out to leave the world they are visiting.