That will no be big enough. What's the length and width of the tank?
A good tank to start with would be a 2ft or 3 ft. Just like fish, the bigger the tank, the easier it is!
That will provide enough room pools and bits and pieces while still allowing the crab to move about.
Is there a reason why you can't get a bigger tank? If it's money maybe getting hermit crabs isn't for you? To get the most out of your crabs and well setup tank will be good.
If you do get some, 90% of the time they will walk around for a day or 2 and then go underground...so you just have to wait.
Have a look around at garage sales and and on ebay for cheap prices. My hermit crab tank was setup for under $50 because I looked around for bargains.
Daniel