Hi Lee,
You haven't said if you intend to work for yourself (self-employed) or for a firm.
If you intend working for yourself then you won't need the NVQ3 - especially if you intend doing 'housebashing', as you put it.
The NVQ3 will be required if you intend to work for someone else, as they will expect this qualification - as will the JIB if you want grading from them for site work etc.
This is what I would aim to have in the form of qualifications if I intended to set up my own domestic/commercial firm:
C & G 2330 L2 & L3 - This should give you the foundation knowledge.
17th Edition - You should have this qualification regardless - you'd be surprised what the 2330 doesn't get round to or 'skims' over.
C & G 2391 - To fully understand, (and prove your competence in), inspection, testing, form filling etc.
If you haven't had a lot of testing experience, use the 2392 as a stepping stone - although it's very similar to the 2330 L3.
Scheme Membership - take your pick - there all as bad(good) as each other.
You may then want to specialise, and take further courses, but the stuff I've listed above certainly qualifies you (on paper) for 'Domestic' work............the other requirment, of course, is
competence.