I have no experience with either adopting a semi-feral or with incorporating a second cat into a one-cat household, but hooray and congrats on being adopted by an orange boy.

Oh, and this thread is useless without pictures.

I have um, several cats (five at the moment), which means I've introduced cats to each other several times. It helps if you have a separate room you can keep the new guy in for a while so they can get used to each others smell. Then you start letting the new guy wander around supervised. After a things seem mostly calm between them, you can let them roam freely.

Sometimes it's easy to mistake cat play for cat fighting.

P.S. There's a lot of cat introduction threads on AskMetafilter.

I got a lot of help by reading the cat intro threads on AskMe and then also from the documentation I got from my local SPCA (hint: rub both kitties down with a sheet of Bounce fabric softener so they'll smell the same and thus greatly reduce the "introduction" period!!!) when I adopted my new little one. The one unfortunate thing is that Livia, my once feral 2 1/2 year old kitty is obviously going to be smaller than Augustus, my new 6 month old kitten. He's been very assertive. Today he learned how to jump up on Livia's favorite lookout windowsill perch and Livia is NOT happy. It seems that as soon as they start getting along, he figures out some new way to assert his dominance and we start all over again with fussing and fighting. There was also some spraying behavior early on--oddly enough on both of my shaggy bathmats--but I'm not sure who it was, and fortunately it stopped fairly quickly.

Sigh. Kids.

Do not do what I did when I introduced Ricky (street cat) to Bella and Barry (pampered softies who I'd had since they were 8 weeks old) and just shut them all in a room together so they would 'get on'.

They didn't. Not for ages. And when I eventually plucked up the courage and opened the door they ALL hated me.

But this was 20 years ago when I didn't know a lot about cats.

My opinion is that they'll have troubles in the beginning -- turf wars and such -- but that they'll work it out eventually. You can't do it for them.

Do it!

I guess it all depends on the cats. Thinking back over the years, most of them were pretty going. When I first introduced Teddy, my other two cats were laid back, and he was the aggressive one. My cat Pumpkin liked him immediatley, but Charlie could take him or leave him. I didn't have the luxury of a separate room, so they were all just thrown in together in the house.
This past summer, with Pumpkin gone for a couple of years, we found our kitten Jersey. We kept her seperate for a week, due to the fact that she was so runty and had an upper respiratory infection. When she was allowed out, she was hissed at, and occasionally swatted at, but now she initiates play with Teddy, who outweighs her by at least twelve pounds. Charlie, on the other hand, is a wimp, and he runs from her.
Congrats on getting adopted!