200miles a week minimum in base period. 10-12 hours. You will get better the more you ride. Even at a low intensity
so 200 miles a week at 20mph average at low intensity?
To the opening post - you do not need to do 200 miles a week by any means, better to think in terms of hours available to you.
Low intensity has a place in training - but the traditional advice of lots of miles at low intensity is bollox. If you're aiming at doing hour long crits, being comfy on 4+ hour rides at a slow place will not do all that much for you.
Quality > Quantity every single time - be as specific as you can to your racing demands