I get why you are asking these four questions, and along with seconding what /u/notoneregret had to say, I'll say this.
Answers to your questions are difficult to offer, because they are all situationally dependent on you.
1. Will a woman want a 25 year old man? Depends on the man and it depends on the woman. Some women are in the bowl for sexual reasons and financial reasons, some aren't. If you are attractive, kind, interesting and sexy, and if you are compatible with her, than intimacy shouldn't be an issue, inside the bowl or out.
2. This is a budget issue - as for "affording a hot SB" - what is your definition of hot? Where do you live? Are you the type of person who gets along with a variety of personalities? "Hot" is subjective, and there are no sure things, even in sugar. Some SBs have no idea of their appeal, and your discussions about allowance will have a lot of decisions/factors at play. If you want to look at ladies strictly for their "hot" factor, which is totally okay, you might want to look for escorts, because they have transparent "rates" for you to review. In sugar, it is a bit more complicated. None of us come with a sticker.
3. In my experience, an arrangement comes with intimacy, and that's a part of the culture of the bowl. You'll get a lot of opinions here, some conflict, but that's something we all can agree on. Unless it is a stated platonic arrangement, sexual intimacy comes with arrangements.
4. Define "real" relationship. Vanilla? I only have one friend who married her SD, and they are currently having issues not related to the bowl, but in my experience, yes, it is very rare. Most SDs and SBs have strict and transparently discussed (I hope) boundaries, and let someone know up front what they are, and aren't interested in. What "real" is is really up to you!
Good luck.