If you are going to use a manual fuel pump to fill the A/C, count how many turns you have to make while filling your tank, then fly. When you land, refuel and count how many turns it takes to have the fuel come out of the exhaust tube. This will give you an idea of how much you're burning and you can also get a rough estimate of how long you can stay up, with throttle management of course.

I had to replace the stock tank in my Avistar after I nosed it in too hard. It split the forward seam and it leaked through to the forward compartment. You might want to think about making a hatch to get at the fuel tank in case you need to do any adjustments or replacement. I put in a Sullivan seamless 8 oz in mine and I get about 15 minutes of flight time at 1/2 throttle and no aerobatics. It leaves about 3 "turns" in the tank at landing. I have a .46 FX in mine, the predecessor of the .46 AX.