What is the general order of subjects of which the ATPL course follows? what would be the ideal first book for me to study?
They don't really follow any order, in fact there is a lot of overlap of different subjects.
Most residential courses are 6 months on a rolling basis, so you come in to start your first 3 month set while the last guys are doing the same subjects as their second 3 month set.
There's plenty of material available, and if you want to part with some cash you can get the oxford computer based training programmes from transair or pooleys. I never used them myself, but people I know who did always said they were good.