Hello Ben
My recommendation would be for you to find a local accountant, very few can do everything themselves when they have a company so finding an accountant who can keep you on the straight and narrow will be invaluable. One who will invest a bit of time at the start and can reel of with confidence what happens with cis is necessary - with paye/cis miltary type planning is necssary due to the short timeframe between month end (5th month) and final reporting and payment dates (about the 19th) in hmrc rules dictate that a contractor can wait till the 19th to give you the information you need to submit that same day - crazy but true.
Its a technical rule of that you need to have a paye scheme if you either receive income with cis with tax deducted or make payments to subcontractors, that then brings in the relevant rules that apply where the scheme exists and there are no payments . Where there are payments or income deducted then this information needs to be submitted to hmrc every month.
The technical rules of how everything works is all available on the hmrc website although i am not joking when i say its ridiculously complicated for what is essentially the same type of transactions that don't specifically need to be reported virtually all other types of business