I've moved tanks across town and across the country (CA to OH - me, the fish and the birds in the front of a U-haul - now that was fun!
) Actually they'll be moving again in the next month or so, about 50 miles.
If the tank will be empty for awhile, just clean it all up and set it up later, just like a new one. Give it a nice long gradual cycle, add a few fish at a time, etc. If sooner - a week or so, then try to keep as much bacteria alive as possible in the filter media. If you're changing out the gravel though, and cleaning the tank, you might just consider it the same as a new cycle.
As far as undergravel filters, not really in favor anymore. Get too gunky underneath. They do a good job of holding the good bacteria, but can lead to pH crashes if you're not careful. Also harder to plant. I use hangon in addition to sponge filters.
As far as the catfish, I had a pleco that survived like that. The tank went bad, everything died, I bailed it out to the last couple inches of water, and left it there awhile. Then when I went to dump it, found Mr. Pleco alive and well.