I make that 280 US gallons based on 60 x 36 x 30 which you mentioned elsewhere or 336 US gallons at 60 x 36 x 36. Either is a NICE tank for Clowns.
You are going to need a lot of filtration on a tank like that. Probably two big cannister filters at least, plus some internal powerheads for water movement would be ideal. Depends on what products are obtainable in Trinidad.
For the substrate I would use sand. You need an inert, smooth, non-calciferous sand. Usually such stuff is sold as Play-sand for kids play-pits.
Here's my 6 foot tank set up last October. There are some other posts on it since, but i can't find them.
http://aquaweb.pair.com/forums/archives ... view=96568
There's a Rena XP3 cannister in each of the outer cupboards in the stand, plus an Aquaclear 500 HOB on the left end rear. You really need more throughput because of the larger capacity. Emma is your best bet for equipment advice because of her experience with a monster Clown tank.
Steve and Emma have some big filters on their tank.
Martin.