Multiple profiles on same machine with different regions

If the main thing you're concerned about is online multiplayer, then yes, all accounts on a single PS4 can play online if at least one if them has an active PS Plus subscription, and that PS4 console is set as the PS Plus account's "Primary PS4."

From Sony's FAQ:

PlayStation®Plus benefits available to other non-subscribing users on your Primary PS4™:
- Online multiplayer (subject to any parental control settings on sub accounts)
- Play downloaded games purchased with PlayStation®Plus discount
- Play downloaded IGC games

PlayStation®Plus benefits not available to other users on your Primary PS4™:
- Purchasing PlayStation®Plus discounted products from PlayStation Store
- Online game save storage
- Auto patch download
- PlayStation®Plus exclusive early access to game trials

Yes, both of them.

On PlayStation 4, if the "Main" account of the PS4 has PS+, all other accounts on that device (up to 16, no matter where they says they're located) can play online, and you can play any downloaded game on the device no matter with which account you bought/downloaded it with; i.e. I used my asian (secondary) account to download Ace Combat and play it on my US (primary/main) account.

If you use the asian account to play, you will earn trophies but in that account, not on the US one.

Other thing is, you can't copy the save file for a game from one account to another, well you can copy it to a usb when logged in with asian account for example, and then copy it back on the US account, but you can't use that save file to re-earn those trophies on the US account. I've already tried it, we laughed so hard when we saw a notification stating "You did not earn a trophy" when I tried lo unlock one.