If House opts out, Marbury is probably your best option at backup PG. IF House stays, you are better off looking for a guy that has a bit more size and D, so you can play him with House without being super duper undersized.
You can get away with a backcourt of Steph and Rondo or Eddie and Rondo. I'm not sold that Rondo and House can work except for occasionally against teams with two small guards in their rotation.
If Grant Hill (who I consider the best option) is brought in as the backup wind, Starbury is probably a bit worse of a fit (because he's not a true 3pt threat to compliment Hill and also creates much value off the dribble) than House. But Hill's shorter jumper is fine, and Marbury had started to knock down threes pretty well before he was banned in NYC, so its possible it could work out. Posey's play in 08 is probably the perfect wing compliment to Marbury off the bench.