Sorry but at least its a slow leak. Glad it was able to be mended.
The tub will help with the transfer. A power head and a heater will be fine while you move things around. Don't worry about the canister for that period of time. Rinse it out with some vinegar/water.
May consider a new bag of sand and a little of the sand from the current tank. Moving sand beds without washing them can be problematic. If you vacuum your sand you should be ok. If not, I personally would not move the entire bed.
Account for ALL of your fish whenever you move rock. Some like to hide in them and you could trap, smash or forget it while rock is out of the water. On that note, try not to keep the rock out of the water for too long.
Only other thing I can think of is check the stand and make sure its level before you fill up the new tank. If it isn't, level it. This is probably because it is a used tank but an unlevel tank can result in a leak.
Good luck with everything.