What happens next? Does does a new mayor take over? When I killed him I thought they made me mayor. Being the fact I can't being in mayor election pissed me off

Yes.

They appoint his secretary Mayor.

I can't find the guy after the first meet out front. Where does he hide? I've been meaning to kill him too for forcing the ghouls out.

Not really sure where he goes. But are you sure you want to end up fighting everyone in diamond city

I usually see him up in his office........ If he isn't there, start checking closets.

But where's his office? I was all over that town looking for it.

Does it really make the whole town hostile to kill him? Even a secret sandman kill?

he tried to shoot me so piper and I dealt with him, then his secretary went hostile for some reason too. . .piper dealt with her though.

His office is up in the press box. Turn left immediately after you enter the stadium. There's an elevator that takes you up to his office.