Thanks for the comments and suggestions so far! Yeah, I haven't ruled anything out. I did get started on the cross-bracing but ran into a couple of problems ... mostly, the joists aren't sitting perfectly square so a 2x10 cut to the right length doesn't fit right! I end up with gaps on the diagonals.
Well, and, well, I guess I didn't do enough cross braces because it didn't seem like it was helping at all.
@ Gools - I did consider front access but (for better for for worse) I have decided against it for now. I'm thinking of trying to make this along the same lines as untamed's tank or Superfudge's tank - on the viewing side there is only viewing. If you've ever been in my basement you know that it's a howling sensation of fan noise, pump noise, overflow sloshing .... in this project I want to be able to hear the tank as little as possible in the main room. I'm even thinking of putting in sound insulation into the framing to this end.
I guess I haven't shown much details about the stand - so I guess that's the next few things I'll try to take pictures of. There is a catwalk along the back edge so that I can stand with my feet at the same level as the bottom of the tank - which should help some. I'm only 5'9" (or thereabouts) so reaching into a 30" tall tank is a challenge anyhow.
@wickedfrags - yeah, it may only be a temporary thing anyhow. The main thing though is that it will work to get me going - down the road I can look at building a proper sump. The costs associated with a tank this size are more than I'd like, so to compensate, I'm phasing in purchases for some things, and making do with what I have for other things in the meantime.
Anyhow thanks all for the comments! Hopefully having this thread open will be a motivation to show progress in a more timely manner from this point forward!