1) and about bad words and trolls?
2) What best way to do this? Google play services? B4J server?
1. is always an issue. you would also be surprised what people come up with to have their name look good by using all sorts of weird characters you've never seen before. This can be prevented by locking it down to just standard chars & numbers.
2. if you have some hosting already I'd just do it in php+mysql.
on the other hand that google thing has the benefit that they login already (if they can)
so there's no issue like when 2 people want to use johndoe as high score name.
not sure if you can use google play services on ios aswell to have a global OS independent leaderboard.