Regarding the surrounds...
I can't say it would be BAD, but it's generally a good idea to stick with one line of speakers for your setup so you get a consistent sound. That way, when a sound pans around the speakers, it will sound the same on all of them. If you have a speaker from a different manufacturer that has a slightly different character of sound, then it won't have a good, continuous sound.
As far as paintability goes with the speaker wire, I don't know. I haven't personally used it. I would recommend that you email Parts Express. It's only .09" thick, so it shouldn't stand out too much, especially if it's under some thicker carpet or behind a baseboard.
I'm not sure about cost on having an installer come out. But the person to call would either be a generic low-voltage wire installer, or a HT installer. Just look in the yellow pages or visit one of your local shops that does custom installs (not something like Best Buy) or sells HT equipment and ask around. They should be able to point you towards a good local guy.