How many respondents do you have at this moment? How many respondents do you think you need to be able to generalize the results?

You should take care of the validity of your research though; I'm not sure where you are collecting the respondents, but if all your data comes from Bitcointalk.org users, this has negative effects on your validity. (I can imagine that Bitcointalk.org members for example use their PC quite often and therefore have software wallets (and know how to use USB-sticks for back ups etcetera. There might also be people with less knowledge of PC's which only have a hardware wallet or a mobile Phone to make use of their bitcoins. The latter group is not yet involved in your research).