SDM,
First of all, we need to correct what seems to be a slight misunderstanding on your part. The choice is not "modular" or "full time" as you seem to imply (viz. where you say "whether... [modular studies]... vary much from going full-time").
The choice is actually modular or integrated. If you choose the integrated route, you will have to study/train full-time. If you choose the modular route, you can study/train as fast or as slow (within reason) as you like. It is perfectly possible to follow the modular route, but still to do so full-time.
Ok, that's that cleared up.
The vast majority of us have followed, or are following, a modular course. Many of us are doing this part-time, myself included. There is absolutely nothing wrong with it - in fact, it is almost certainly the best way of training if you feel you need to keep hold of you current job.
How understanding will your boss be if you want to take extended periods of leave? If you have a boss who is not understanding, or if you choose not to tell your boss what you're doing, you will have to plan your holidays over the next few years very carefully to ensure that you can get time off for exams, brush-up courses, and periods of intensive flying training, but that is the only complexity with the route you are looking to follow.
Good luck,
FFF
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