When I had something set up in a crawl space, it was in a 2x4 hydro runoff tray that was set on sliders along the floor so I could just pull the tray out of the space like a drawer.

Flowering under T5s is certainly possible and you may actually be pleasantly surprised at your harvest- I've seen it pulled off nicely, and the biggest bonus is that you can run in a small space and not worry about the plants getting too large, or too close to the lamps. See, with a HPS you have at least 18" of dead, unused space between the lamp and the canopy, to avoid scorching the plants or even a fire hazard. With flouros of any sort, including plain shop lights fitted with T8 'daylight' tubes, you can get RIGHT UP to the lamp with no danger.

Don't worry about flushing. Just re-pot on a schedule so that the plants are always growing fresh roots into fresh soil. Read the 'continuous canopy' sticky in basic. And be extra careful not to over-fertilize, remembering too that plants under flouros feed relatively weaker compared to their HID-grown cousins.

Good luck.