One strategy is to target a USD value for your bitcoin holdings (especially if you're planning to retire in the US on the basis of bitcoin holdings) and then set (m,n) so that you're periodically selling m% of your holdings and buying US$n worth of bitcoin (obviously netting those two out).  E.g. you'll eventually have US$1m if you're selling 0.01% and buying $100 every month (you'll only be net-selling if your bitcoin holdings are currently above US$1m, but as long as the bitcoin price isn't monotonically decreasing over the discrete transaction times, you'll most likely build-in some trading profit as you bought more when it was cheap thus reducing your cost basis)