Still too much of a list.
So, are you set on hermit crabs? I just don't know what kind of herps could live with hermit crabs, but the list of fish that could live with them is quite large.
In this case I would not build up a land area- far too much of the tank would be 'dead space' filled with gravel. Besides the waste of living space, it would also likely lead to the formation of anaerobic pockets, the source of deadly H2S gas.
Instead, build a platform. This can be attached to the sides of the tank or supported by some sort of columns. You can still have a gravel ramp- just silicone the gravel to a piece of plexiglass or other material.
Hermits, if I remember correctly, need both fresh and salt water to drink. So, the main tank could be fresh with a container of saltwater on the platform, or vice versa. Are you interested in a biotope? The most common hermit crab, Coenobita clypeatus, is from the Carribean, so you could set up a Carribean biotope with lots of mollies and Carribean killifish.