Instead of a sync cord for your flash, you might want to try wireless. Go here and have a look:
I have those triggers, and they work very well. As cheap as a cord, too.
If you want to leave that cheap UV filter on your lens while you're not taking pictures, fine. Just remove it before you take the shot. You want to see if it degrades your pictures? Just prove it to yourself. Find an interesting landscape with lots of detail, then take pics with and without the filter. View them at 100% and check the differences.