need some help

hello i am in the middle of making a game in unreal engine 4 but need a little help.

im trying to create an open world with maybe 10 are so islands but dont know where to begain. do i make different terrains for each island and put them to gether? (if so how?) or do i create one big terrain and make islands off of that? (if so how big should i make it?)

also im looking for people to create music and characters for me if anyone is interested.

(if this isnt the right place for this does anyone now a place i can get help from?)