[wingers]

In one race you'll probably use something like 1500-2300mAh. You should never flatten the cells so if you charge up after every race (highly recommended) then you'll need LIPOs that are 3000mAh as a minimum. As you've already seen, almost all of them are larger than that so should be fine on that front. Going for higher capacity cells can provide a bit more power, but only if you go for the more expensive cells (with high "C" ratings) and it's likely that you'll have worn them out before you need the power anyway so I wouldn't worry too much about that just yet. You also might want to swap between shortys and saddles so don't spend a fortune on the first sets of LIPOs. Once you know what format you want and are getting up to speed with it all then some Thunder Power/Nosram/Intellect cells would be worthwhile. There are plenty of others too but they're all going to be about 3 times the price of the cheaper cells.
One thing I would definitely suggest is getting two sets of cells from the outset as there isn't really time to charge one set of cells between races on a club night. You'll want to have one set on charge while racing with the others and then swap over for the next race. Doing it that way gives them time to cool down properly before recharging too so will make them last a lot longer.

Wingers