Well, ... if you do decide to use a single tweeter with a line of RS150's
1. you'll be losing out on half the fun if you don't pick an efficient enough tweeter . No point padding down a woofer or tweeter line excessively.
2. Of course, a tweeter line will sound different from a single tweeter, but not necessarily better or worse. One thing you must realize though is that a single tweeter's output will drop faster with distance compared to a line.
2. don't worry too much about all the talk on the web about ribbons etc. Just do it. At the worst, don't drill the tweeter holes and just tack on a single suitable tweeter temporarily. If you think you might like a tweeter line better, drill some more holes.