Volume, I would tend to be on the lower count, because otherwise, you are going to wind up with an index full of .01-.10 stocks that are so-so, and exclude some of the best OTC's with good managment that resists dilution.
If you look at a stock like BMKS, with 144,000 daily average, that's fine, it should be on the index. Now, XNET, has a daily volume of 36,000, so a higher volume average would exclude XNET.
However, BMKS trades at .015/.02 and XNET at .27/.32, which means that BMKS trades on daily average $2,520 worth of stock, while XNET trades on daily average $10,620 worth of stock.
So, probably a combination of a lower average daily volume, combined with a minimum net dollar amount traded daily is your best bet.
imho, Jerome