HCA: Hermit Crab Association

I'm a new crab keeper; I got my crab in September and he's currently in a 10 gallon. I would like to upgrade to a larger size so I can get him some friends and I am really liking the idea of having a front-opening tank, such as the exo terra. I've read about some issues with them when housing hermit crabs so I wanted some clarification.

I am currently looking at an 18x18x24h" with a piece of plexiglass in the front to hold deeper substrate. Would this be enough room for my current crab (medium) and 2 smalls? How long would it take for them to outgrow it? I don't want to have to buy a new one in 6 months!

I plan to put glass on top and close the air vents with plastic or glue. I've seen this done with toppers, but does it work well enough if it's the main tank?

I have so many more questions but I guess I'll start here!

Thanks.

that size tank is 30 gallons, I think.
Here is our guide as to how many crabs in what size of tank, depending on their size. I had two crabs in a ten gallon for 2 years, then in a 20 gallon for 2 or 3 years, then into my current tank.

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