Porting implies access to original code, so you're effectively looking for someone who would code Brothel City pretty much from scratch, which will be very time consuming and very tedious if you want the end result to be as close as possible to the original. Unless you have every Brothel City design meticulously documented, and original programmer stuck to it to the letter, end result may be way off from the original without a lot of extra time.
Steam doesn't require dedicated version of the game and what you have already could be released there without a problem, but... last I checked and IIRC, Brothel City was not only unfinished, but also pretty buggy at later stages of the game... don't remember the details now, but I think some of them were pretty serious and/or game-breaking. You'd have to be very careful what and how you do if you'd release current version on Steam, especially considering you want to code it from scratch.
Also, don't think releasing the game on Steam will magically solve all your problems... yes, it has a massive reach and potential gains, but competition is also massive, and you won't be competing with only other NSFW games, so it won't be easy to get noticed.
And last but not least, to afford potential programmer you'd probably need to convince people to crowdfund a reboot of a game which wasn't finished in the first place, which I think will be very hard.
I sympathize with your situation, liked Brothel City despite its shortcomings, and I wish you all the best, but I think someone should give you a reality check.
Just my 2 cents.