can a priest still remain a priest if he dosent have people attending his chruch?
Yes a priest is still a priest even if people do not come to his church. Some priests don't even serve in a church. There are priestmonks who become hermits such as St. Seraphim of Sarov or Elder Cleopa for example who were bestowed with the grace of priesthood but spent time alone living a solitary life but they were still priests. There is a rule though I believe that a priest cannot serve Liturgy if there are no people present; there needs to be atleast one other person present.
what if he turns people down?
I'm not sure what you mean by this. Like if the priest doesn't let someone come to church? If they were doing that for no reason then they may just be a "bad" priest but they would still be a priest.
is it true that you are not allowed to do a sunday service after 12pm?
I've never heard of a rule like this so I can't answer this one.