if i was to apply for double or multiple entry visa

i will be traveling by bike. is it wise to say that im going to cross the chinese border to get to mongolia to ulaan baatar (via urumqi but i will not mention that ofcourse) just taking the train or bus or somtehing. and from there on travel to being shanghai, honkong then back in to china to get to vietnam... obviously i will leave the last part and say im going back home after that.
which is why i need multiple entrys and even if i get double can i apply for a new one in hongkong then.