Its basically up to you how you it matey. You need a PPL then you need to do the atpl or cpl groundschool before you even think about CPL , and in my experience this is certainly the most rigourous and taxing part of the whole affair . You definately need the hours that is set in stone , a night rating is also something you will need if you're going for an atpl as is a multi however you dont need as multi to do a cpl but some places do it as a joint course and offer discounts .
In short to hold a frozen atpl you will need
PPL
Hour Build
ATPL Ground exams all 14
Multi
Night
IR
andfor most employers an MCC
There is a lot of debate on here regarding the IMC do a search and see what suits you personally.Dont be swayed by the doom and gloom merchants if you wanna do it then do it it will make you a better pilot , however if your doing the whole thing one after the other then dont bother with IMC as it wont be long before your IR all being well