If you are not going to worry about fees too much, I think the best way is to do it daily, so you are averaging at different prices more and more compared to just one price every week. That's if you have the time to cover it all and understand why you are doing it in the first place. Maybe automate the continuous buying of BTC and stick to a tough time so it could be an experiment to share with those interested in it.

I hope you can update us here with what you plan to do.