Unless I am anticipating that I will need the money relatively soon, or I simply don't have a great deal of confidence/conviction on a stock, I don't really set a limit on how much of the float I would be willing to own. Float/unrestricted share counts can change so quickly in the OTC that my 5% ownership of the float today might end up being just a barely visible drop in the bucket a month from now.
NBLD is a good example of how liquidity and investor interest in a stock can change so dramatically. For much of the year there was very little volume and interest in the stock. That completely changed in a matter of a day or two. So sometimes I am reasonably comfortable in taking large positions in shells/situations where there is almost no investor interest. Investing history has shown that today's "bag of garbage" can be tomorrow's gem.