1.PokeMMO is completely safe.
2.The current regions re Kanto, Hoenn, and Unova.
3.Refer to this short guide to download PokeMMO: https://pokemmo.eu/downloads/windows/
4.Yes they can follow you if you have a soulsilver/heartgold rom in your rom folder, but Gen 5 pokemon do not have follower sprites.
5.It depends on who you befriend. There will be nice people and people that will try to scam you (which is now against the rules), but you can contact a staff member and they can help you trade evolve.