To start the ball rolling, I think whoever is named Nats President will be swarmed by prospective GM's.
Not often you get the chance to take a decent roster and add 30+ MIL worth of talent in one season.
Thats said, the potential both for solidifying the Nats as a contender for the next few seasons and creating a complete disaster may be there in about equal probability.
With the mediocre FA crop, Nats will likely be trying to upgrade by trading players off the MLB roster. I would think almost anyone may go, which opens up a lot of potential for mistakes.
What you hope is both the new owners and GM don't get too hung up on establishing immediate legitimacy by going for the big splashy acquisition (think Mets).
For example, you get the feeling Manny Ramirez could be acquired and he certainly qualifies as a superstar. However, it would likely take two starting players off the current roster - for example Vidro plus Church or Wilkerson and likely a prospect) and its not clear Manny would be the right guy for the Nats.
Same with Johnny Damon. By default he's the biggest name FA this offseason and there will be a temptation to sign him just to prove Nats are serious about winning. He also may not be a very good fit.
I dunno if there is much point in speculating on GM's as it will depend on who is president and who is available. I wouldn't rule Bowden out, but he's sure not an automatic hire.