So I take it the stray is back outside, and that the concern isn't about Panda getting along with him, just the litter, jumping on counters, and scratching?There are plenty of ways to avoid having problems:
1. If you use clumping litter and scoop the clumps at least twice a day, there shouldn't be any smell, even using a non-scented litter.
2. I've had 2 cats jump up on the counter, but I picked them up and placed them back on the floor. They both tried 3 times, and got put back down on the floor, and stopped jumping up there. If that doesn't work, there are sprays you can get that discourage cats from going wherever it is that you don't want them to go. You can also try squirting water from a spray bottle. Or putting something on the surface that they don't like the feel or sound of, like aluminum foil. I also heard that putting empty soda cans along the edge would discourage them, because they'd fall and make a lot of noise.
3. Get at least a couple of scratching posts - maybe one vertical and one of the flat ones, like the corrugated cardboard ones and put them in places that are easy for them to get to. I've had 3 cats and none has ever scratched any of my furniture. If it's the fabric on furniture you're concerned about, again, you could try one of the sprays, or you could put a throw or towel over it. There are also these things that you can put on their claws. And you should trim their claws regularly.