MM,
As far as I recall the following applies,
be careful because jb5000, is talking about an integrated course, but from your post you are looking at modular.
The modular route does unfortunately impose the condition that prior to sitting the ATPL exams you must have completed a recognised distance learning or full time course. I have worded it so because these training organisations will insist you hold a PPL prior to commecing the course, but in reality the books are commercially available (at extra cost from Transair) so theoretically you could buy them and start your studies early. However beware as the books are very hard going in terms of volume of material and they are generally sold for experienced pilots to convert existing qualifications, so they are lacking a support network. Without this I fear you would be overwhelmed very quickly.
A distance learning course will cost you a little under £2000.
A more normal route is as follows:
Medical
PPL
ATPL's concurrent with Night rating and hours building
CPL
Multi and IR combined
MCC
This is in effet a CPL/IR with the neccesary bits bolted on becoming a fATPL. There is in fact no such licence as an fATPL, just a CPL/IR with all the multi crew training, multi engine ratings and ATPL exams added.
My advice would be don't bother looking at the books until you have your medical and PPL. Lastly there is no time limit between starting you ATPL studies and the first exam, but once the first exam has been sta you have 18 months to complete the rest and then a further 36 months to obtain your CPL and IR from passing your final exam. Hope this helps,
Obs cop