Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Go for it the way you posted. Get it all done in one day.
I also have doubts about the substrate coming up in cake-like chunks, but don't worry about that. Do the best you can with the plants and substrate, then cap it. When you are ready to fill, put a plate or plastic bag over the substrate and run the water in slowly, letting it seep into the substrate. This will minimize clouding.
If the fish are warm enough, OK in the bucket, then allow the filter to run on the new set up for a few hours to clear the water (if needed). But if the fish are not OK in their bucket, then go ahead and add them sooner.
Do not add the water the fish were stored in. Stressed fish produce excess ammonia, and you do not want this going into the new set up. As long as the new water matches the old (GH, KH, TDS, pH) the fish will be fine.