In response to your question about pre grown plants from modules – correct, these are just seeds that have been planted in plugs/modules and have germinated and grown into little seedlings. Charles raises almost all his plants this way (Carrots and Parsnips being two notable exceptions), as he gets much better results. The seedlings are more resilient, and less prone to insect and wildlife attack by the time they are planted out, than seeds straight in the ground.
Charles uses a dibber, of approx the same diameter as the plug, which saves time. Dib a row of holes, pop the plugs out and simply drop them in the hole. Its better to plant the seedlings slightly deeper than you’d maybe expect, only just above the level of the surrounding soil, as this gives them extra protection as they establish. And no need to firm them in and backfill, you can just drop the plugs into the dibbed holes and they’ll grow fine. The beauty of Charles method is he has refined it over 40 years to cut out all the unnecessary time wasting work, making it a much more efficient use of your time.
Rotation – Charles does advocate this, but perhaps not as rigorously as other say. If you are double cropping a bed in one season, you don’t need to rotate. But a good idea to do so from season to season when possible. Established perennials stay where they are of course.
Fine to dump the compost and simply plant the plugs straight into it, as long as it is well rotted (approx 1 year for farmyard manure), or not too hot in the case of green manure. Green manure will probably have slightly less nutrient value than the humus rich option. A mix of both would be good, but should be fine on its own, it looks like decent compost on the link you provided.
Every year, you just top up the compost once. a few inches on each bed. No other fertilisers needed
Good luck with it.