Hi, that stocking, can you list the numbers you have of each fish please? Fish of some species need to be kept in groups of a minimum number, since they're social or schooling species. If you're not sure what kind of species you have, like which kind of cory for example, then please post photos and someone will be able to ID them for you!
The amount of species you've listed already though really is a LOT of fish. That's not a light stocking, especially if you increase their numbers so they have the right schooling sizes. But it's important for their welfare that they're kept in the right group sizes, so please, give as much detail as you can!
You said you want more bottom dwellers, but you already have a good number with the cories, a pleco, a shrimp and a shark. How long ago did you get the shark, and do you know what kind it is? Red tailed? rainbow? Bala? Again, photos please if you're not sure! It's very important to know, since some species sold as 'sharks' (which aren't truly sharks, that's just a common name for them) seem fine in a community tank when young - and they are sold as juveniles so would have been young when you bought it) but become much more territorial and aggressive once they mature. They can terrorise and even kill their tankmates, so it's crucial you know what you have and what it can safely live with.
A fine sand is definitely much better for many bottom dwellers, but especially so for corydora catfish, so yes, that's a great idea to choose that for the upgrade.
The transferring fish/tank/water part I'll go into detail with in another comment once the stocking questions are sorted