If it's leaking just from one seam, like the bottom, then you most likely just need to repair that seam, so you wouldn't need to take the whole tank apart.
As for the weight and size of the tank, in order to remove all the silicone, clean it, and then re-silicone the tank again you'll to move around the tank, even laying it on its side, otherwise it makes it harder to get into it and do everything, especially when you're doing the bottom seam on the tank, which if you need to reseal the whole thing it's 6'. A large heavy tank can make doing that harder.
Bottom line, everyone wants to save money but the most important thing in a setup is the tank. I'm not sure I would want to play around with a very large tank unless you're 100% sure you can do it.