You can call a listing agent but the first thing they will ask is "are you working with a realtor" and if the answer is yes, they will ask you to have your realtor call for a showing. This is not to say you cannot use the listing agent to purchase the specific house abd not uxe your own agent, but in hindsight it is good to have your own representation, as the listing agent works for the seller and that is where he/she fiduciary lies. Does this make sense? I would happy to clarify and answer more questions if need be.
Correct, you will need a trustee assigned.