I think hour building whilst studying is fine (not at the same time as mentioned earlier
).
But as BlueRobin states, don't just spend as little as posisble in 150/152's and that sort of thing. Get in some complex aircraft, tail draggers and that sort of thing. the hours will be much more valuable and more appealing for the log book than chip as chips trainers.
Do you multi rating, that gets that out of the way and they are quality hours.
Then their is the IMC or wait for IR argument. Personally I say if you have the money do the IMC, the hours a much more quality hours than VFR bimbles. After IMC try to get as much instrument flying as you can done, especialy instrument approaches
In basic terms if you want to hour build while studying go for quality hours over quantity hours.