Welcome to the forums!
Tough question; you may be able to resolve the SL (student loan) issues, maybe. I'd certainly at least look into it in the rebuilding or student loan forums, I know absolutely nothing about SL's so I can't offer any advice personally.
The problem is the market is going to be moving over the next few years: all the talking heads are suggesting rates are going to go up, but economic data is seriously mixed. Personally I hope we just pick a direction in the near future. If rates go up, housing prices will fall, so that may not be the end of the world depending where you're looking.
If you're planning to have kids, I'd look at where I wanted to raise them, and then look to see if I could get into a house sooner than later. Granted until they're in kindergarten I could make the argument school district and what not doesn't really matter, but I'd at least go looking at options now. A 640+ can easily get underwritten on a loan, and there may be some other credit issues which you can clean up (high revolving utilization for example) as I have a bunch of derogatories from late 2010 which sounds like your time frame (tax lien, some lates, collection) and I just cleared north of 720 on a mortgage trifecta.
I guess as a plan of attack I'd approach it like the following:
1) pull my credit reports
2) see what could be fixed (student loan issues, or other things in your files)
3) fix what I could
4) pull my mortgage scores and see if I could make it work right now.
5) if I couldn't, go back to plan B which is wait a while, just it's hard to predict where we're going to be in 3 years at this point.
That's pretty much what I doing even without the spouse and kids to go on, just I had a longer time to optimize my reports over but I was pretty certain the mortgage market would be sort of flat or ease over my own timeline (starting in late 2011) but now, it's a little more pressing for me to do something right now regarding a mortgage.
