Yep, just keep the top clean and don't let staining things set in long (like bird crap or, in my experiences, stuff from trees). And keeping some kind of a protectant on it will help a lot too--right now we're using Mop N' Glow, as suggested by a few other posters here, and it seems to work better than other things I've used.
As for the tires, you really don't even have to look too hard to find them, as just about every "passenger car" tire you find in the FW's size of 235-70-15 are whitewalls anyway on one side--sure the ones on the car now aren't flipped, black out/white in? We just put new Kumho Touring A/S 795's on ours and love 'em--great tire, especially for this car.
And the deer horns--YES, you can take them off! They should just be attached with little sticky pads underneath, so if you can pull the horn itself off, any remaining glue can most likely be rubbed off with a fingernail or some Goo Gone.
Again, great car!