Many thanks for your helpful response.
With my work/study, I will not be able to start the CPL/IR for at least another 2/3 years. There will be vacation periods were I could do many hours at once as you suggest - but then the issue is that I would end up hitting 100 hours PIC well before I could start the CPL and therefore there could be an extensive period where I am doing little or no flying, thus losing currency. Hence choosing an hour a week or so as a decent compromise.
With regards to the airlines themselves, all else being equal, would you say that the kind of timeframe I use is irrelevant? I've tried looking at the various recruitment sites for the airlines, and the only things I've been able to find are that the CPL/IR should be done together at the same place, a 90% average is needed in the ATPL theory exams, and some airlines also state a need for a certain number of hours in the past 12 months (I think 60 for Flybe). So apart from the last point, there doesn't seem to be anything about flight frequency.