I can't answer all your questions but here's my input:
Firstly, there is a 'Diploma Transition Plan' on the CQI website which provides you with further info. Link:
http://www.thecqi.org/Qualifications/CQI-Diploma-in-Quality/Diploma-Transition-Plan/
I'm completing the diploma as we speak - I commenced the third and final year in September. I'm studying at Blackburn College and I appreciate the discipline, instant tutor support and 'live' interaction with other students which this offers. The structure has been rigid, in that 2 modules were completed in year 1 (D1 & D2), 3 in year 2 (D3, D6 & D7) and 2 in year 3 (D4 & D5 (the quality project)). I found the face-to-face contact especially invaluable with modules D1 (the stats/maths side of things) and D7 (the IT side of things, though it looks as though this will be ditched under the new revision), as I found these quite tricky to begin with and dread to think how I would have coped had I been studying these via distance learning. We complete an assignment per module (hand in at Easter) and an exam per module (takes place in June (with the exception of D5)).
I'd say 2 years to complete the course is unrealistic, unless you have a significant amount of time to devote to this each week? We meet at college once a week for 4-6 hours (term-time only) and, if I'm being honest, I'd say another 2-4 hours of home-study per week is needed if you're looking to do well with this. Even more when assignments are due to be completed and exams are looming.
The following link to a CQI page gives you some guidance regarding the lack of previous experience in quality:
http://www.thecqi.org/Qualifications/CQI-Diploma-in-Quality/Entry-requirements/
Apologies but I can't offer anything regarding the ASQ certificates - I've never seen a direct link between ASQ certificates and the CQI syllabus. Which certificates do you hold?
Personally, I'd advise enrolling on the course. It is certainly favourably recognised by a large number of employers and covers a wide range of quality-related issues (link to the current syllabus:
http://www.thecqi.org/Documents/Qualifications/CQIDiplomaSyllabus.pdf ) which will surely be of benefit and, in a number of cases, will probably prompt you to complete further research of your own, above and beyond the course content (that's certainly been the case with me). I'd recommend seeking out your nearest learning provider who run the course 'in the flesh', as described above. We have a few people on our course who started out with distance learning but found it difficult and prefer this method instead.
Good luck with it all. Just one final point - consider seeking the opinions of Paul Simpson (you'll find quite a bit of his input on this site if you search). He is the man in the know when it comes to CQI info.
Regards,
Mick