If you will excuse the horrendous headline - seriously stop it, guys - Rosenthal had a good article up the other day about the new problem the Astros are facing. With Gattis, Marisnick, Springer and Rasmus vying for 3 outfield spots, and Singleton, Carter and Gattis vying for the 1B/DH position, the Astros are facing a game of musical chairs that will end up with someone without a seat. I'd take this roster issue any day over the roster issues facing the Astros the last couple years, (is there anyone here who can play SS? No?) but still, it's something that will need to be addressed.
I think there is a relatively easy solution, although it might not make one of the new acquisitions very happy. I think the Astros need to seriously consider a platoon in Center Field.
Colby Rasmus has proven one things with an absolute certainty the last few years. He cannot hit left handed pitching. His performance against right handers has varied, from a 95 wRC+ in 2012, to 144 in '13 and back down to 106 the next year. But his performance against lefties has not approached average since 2010. For his career, he has a 112 wRC+ against right handers - not elite, but above average, especially for a center fielder - but only a 77 against lefties.
Marisnick has not had enough major league at bats to judge whether he has a similar split. Last year, his wRC+ was 109 against lefties, and 54 against righties, but that was only 237 PA total, and only 55 against lefties. Still, I think its fair to say he's likely to hit as well or better than Rasmus against lefties. Platooning him, and possibly having him come in late in games on defense, will get his glove in the field and potentially produce a well above average, both defensively and offensively, CF team.
This all assumes that Singleton hits and Gattis is not an unbearable butcher in LF. Those might not be safe assumptions, but if they occur, I think this is the best way to get everyone playing time, while maximizing offense.