you need to completely empty the tank. Plants need to be removed and substrates as well. DO NOT move it with weight in the tank. I've moved my 55 gallon high tech before and the gravel alone is 100lbs. You can not have that weight in a tank and try to move it. Its not the bottom of the tank that is the issue, its the shifting weight and it forcing against the sides. Practiacally all US standard tanks have floating bases so the bottom glass pane supports ALL the weight when full. Also tanks are awkward enough to move when empty. Moving one with a load is just asking for it to slip or get damaged.
For fish I would bag these then place the bags in a cooler to keep them warm and dark to reduce the stress.
Plants: pull them all up. Do this only once all fish caught as things are gonna get cloudy. Place plants in bags kinda like fish, except they don't need water. The bags will stay very humid with the wet plants in them. For the wood and attached plants put them in a big bag. Plastic grocery bag/trash bag. As long as its unscented and just a plain old plastic bag. If I remember right I used black garbage/yard bags for my driftwood.
Substrate: I would leave the tank full till you have all the plants and fish removed. If you have just regular gravel I would then give it a decent gravel vac. If the tank has been running for years there is gonna be a lot of mulm down there. You should suck up quite a bit of it so it doesn't cause issues when you set the tank back up. Don't over clean the gravel. Just get the worst of it and be done. Scoop the gravel into buckets. It doesn't have to say wet, but I highly doubt it will dry out anyway. Your bacteria is in the filter, not the gravel.
For setting back up add the substrate back to the tank when it is completely empty. Then fill it with water. Set up equipment. It will be cloudy and this is fine. Start replanting the plants. Once that is done start acclimating the fish to the new water. Ideally you should only release the fish once the tank is basically 100% up and running. That way they can settle down as messing with the tank is only going to add to their stress once they are back in it.
Most plants take moves pretty well. You will see some die back the first week or two. How much depends on how different the tap water is at the new location and the species of plants. Nothing is set in stone. When I moved my 55 gallon, my stargrass had a meltdown over the new water. On the other hand my huge number of crypts which are a well known species for melting were not phased by being uprooted and replanted in significantly different water
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Here is a simplified picture depiction of when I moved my 55gallon. It was also moved 15-20 minuets away.
1. Take pretty tank.
2. put all fish and plants in giant cooler. At least the ones you can fit lol....
3. Does tank now look like crap? If yes then you are doing a good job
4. remove water and substrate as much as possible. Strip down all equipment.
5. Try to fit everything into the back of an SUV.
6. get everything to new place and wonder how it all originally fit into a 1x4 footprint
7.Add substrate, refill, and begin replanting.
8. Acclimate and release fishes once you are done.
Total time from start to end was roughly 7 hours. Monitor water a bit IMO. Depends how planted you are. I never tested my tank after moving it, but fish will tell you if something is wrong.
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In a newly setup tank that is true, but in the established aquarium it is the substrate that houses most of the bacteria.
