When a new ue4 version comes out, it usually takes a week or two for a new kit version to come out.
Whether it’s 100 or 150 depends on your gameplay of course. Fortnite’s gameplay allows 100. Maybe your MMO’s gameplay would allow more. Depends.
I’ve not modified the engine, no.
All actors have a variable called “Net Cull Distance Squared”, it’s a distance after which they don’t get replicated to others.