Make the water brackish, like 1.005-1.010.
1 should do fine in a ten gallon
Half land half water or make a floating platform.
They eat crickets and other small bugs.
Indian mudskippers would definately like at least on friend. I have 3 Africans in a 20 long right now but I have a 60 I am workiing on for them. Indians don't get real; big but I would think a 20 long would be perfect for 2. Check out Mokomon's old threads and ask Sploke. They both know a lot about 'skippers. They are the ones that got me hooked.
This is my mudskipper tank.
I'd get at least 15-20 gallons for a single mudskipper. Maybe for 30 gallons you can get 2-3 mudskippers. If it's an Indian mudskipper than you'll be fine with a ten-fifteen gallon tank for several. Those shouldn't be to expensive.