7 1/2 X 8 X 4 first try

Check prices from Laird Plastics. I think they have a location close to you. I used the one in Houston for my 2" 4'x8' cell cast acrylic window. Depending on the size of the window, 3/4" could work, but I'd be inclined to suggest you go with at least 1" for added safety.

Look at VLDesign's and JohnG's builds to see what thickness they used.

In regard to your design, whichever way you build it, sticking with standard lengths of dimensional lumber i.e. 8', 10', 12', etc. will save you lots of cuts.

Think Kegerator!

Buy a dorm size refrigerator.

Get enough PEX tubing to coil from top to bottom in the refrigerator.

Buy Uniseal fittings from aquaticeco.com or some other place on the net that has them. You'll need two that will allow the PEX tubing to fit snugly through.

Drill two appropriate size holes for the Uniseals in a convenient location on the fridge making sure it's not somewhere that you'll damage the cooling capabilities.

Insert your Uniseal fittings from the inside of the fridge.

Insert PEX tubing ends out through the Uniseal fittings.

Attached end fittings to the PEX.

Plumb your new refrigerator chiller to your filtration by connecting the PEX to a pump and return.

Hook a thermostat controller to your pump to circulate the water when the temp in the tank is too high.

Turn on your mini-fridge and there you go.

so much tanks!!!

Flexpvc.com is a filtration parts playground. I haven't found a better selection of bulkheads anywhere.

http://flexpvc.com/cart/agora.cgi?product=BulkheadFittingsStandard (the 2" white and black ones are the ones I chose)

http://flexpvc.com/cart/agora.cgi?product=BulkheadFittingScreens (the ones I got are like the black one at the top but for 2" which they have discontinued)

Depends on the pump you're using, but I'd suggest you go 2" out and 1/2" bigger than recommended in. i.e. if they say you need 3/4" go 1.25". What they recommend doesn't take into account restriction from angles in plumbing. I'd also go with flexible pvc in, so you avoid 90's and 45's which add to head pressure.