Someone gave me this site that is specifically for FtMs and their admirers. I haven't had a chance to really check it out, so it may be full of creepy
>-bleeped-<-
>-bleeped-<s, and I don't know how international it is, but I thought I'd throw it out there.
http://ftmloveconnections.ftmworld.net/V3Profiles/
As far as when to tell... I dunno. I keep going back and forth about that as well. From what I hear, most of the time if you tell before they get a chance to know you, they say, "Well, thanks, but no thanks." and move on. (Unless they're into FtMs.)
The danger of announcing it in the ad is that you might draw people who are more interested in what you are than in who you are. But, at least they can't complain that you were dishonest with them.
The guys I've heard from who have been successful in finding a relationship seem to have dated the person for a while, then told them after they were hooked (but before getting intimate, obviously.) The danger in this scenario, of course, is that they might get angry and accuse you of deceiving them. That's where we FtMs have it easier, I think, than MtFs, since neither women nor gay men are as apt to become violent when they find out.
Not the kind of 1st hand advice you were looking for, I realize, but I hope it helped.
EDIT: I just got around to checking out the link above, and it's pretty dead, and badly set up, so don't bother.