1. Royal Purple (or most any synthetic) would be good for you so that you can wait longer between oil change intervals - i.e. just change the filter and you can use the oil quite a bit longer than conventional dino oils. In other words, if you're only putting miles on during the weekends and whatnot, you can get away with running the oil a bit longer without much fear of it breaking down. Royal Purple's literature claims that you can use the same oil for 12,000 miles without worry as long as you change the filter every 3,000 miles. Soooooo, thumbs up on that one.
2. Royal Purple and really, any synthetic oil will NOT cause leaks. Synthetic oils do generally have detergents in them that will clean the engine, and may get rid of sludge and/or buildup. Now, if you have sludge/buildup that is masking a leak at say, the rear main seal, or the oil pan gasket, etc. - you may start to see leaks or drops on your garage floor. But remember, this isn't the synthetic oil causing it! It was already there and the dino oil buildup/sludge hid the problem.
My car had 53,000 miles on it when I switched to Royal Purple last year, and I have no complaints. If you have the money, I say go for it! I was very satisfied with how it held up (Just changed it out about a month ago). Synthetics rock if you can afford them! Mobil 1 or Quaker State Q are also good choices (you can grab a rebate on them at PepBoys and other places and perhaps even snag a rebate on a free Mobil 1 filter). BTW, sticking with Motorcraft oil isn't so bad either. It's a reasonably priced oil and is a synthetic/dino blend if i'm not mistaken.
Hope this helps.