If I have a domain that is trusted with another domain, can i use User Profile Synchronization to sync users in the the Local AD and use AD Import to import users from the trusted domain?
If you have two trust (i think), then you can have sync connect with it. All you have to do is create a separate sync connection with each domain.
also check this for people picker: https://thesharepointfarm.com/2014/01/powershell-for-people-picker-properties/
Yes, you could perform the sync.