Beware that, depending on country and indeed specific university, some will attempt to claim ownership of IPR you develop as a student while studying for a PhD.

Beware that, depending on country and indeed specific university, some will attempt to claim ownership of IPR you develop as a student while studying for a PhD. This isn't across the board, and different institutions have completely different approaches, but certainly in some countries there may be terms contained in PhD funding project. In some countries, a PhD studentship is treated formally as a fixed term employment with contract. In others it isn't. It's worth checking if they have any claim to ideas you create while working on your PhD, as you might want to be very careful to stop having ideas for a while if that was the case... That the topic is unrelated to your dissertation may not be relevant if there is such a clause, but you should probably check this out, in addition to considering the "acceptable IT use" agreement or whatever your institution has in place, to see if they disallow use for personal business.