Would you expect to be asked to teach on a p/t PhD? Combo just came up with my potential supervisor and I wasn't sure what to say as I'd been planning to work (only a few hours a week, research the rest, hadn't factored in time for teaching...)?
Does your studentship require any teaching as part of the contract for doing it? If not, then surely it's up to you if you want to teach. It can be great for the CV, earn more than the min wage and you can see if you like it which is really important if you are even slightly interested in carrying on in academia. If you are not, then it's up to you whether the money works out for you, it may not although I have PhDs that subsist on teaching, seminars, transcribing, bits of research etc.