Query about Wheelie bin CFT designs

Brian,
First of all thanks for sharing so much good information on worms and various worm farms.
I  a lot of very good information from the videos I purchased last year.
After waiting some time, I have finally purchased a 240l Wheelie bin and started looking around for various designs with yours being a front runner. When looking around and searching for bin worm farm, there appear to be quite a few designs that use round vents at the top as well as round access holes rather than the pipes in your design that seperate the worm farm from the harvesting area.
While I like the appeal of the round air vents that pop into a 64mm holes, I am not convinced of a design where there is no seperate harvesting floor that provides more air from underneath and a convenient way to harvest without having to dig out a hole that might not as easily re-fill. 
What would you say are disadvantages of alternate designs where you harvest the worm casting via the access holes?
As per your recommendations I will be building 7-8cm thickness of dry cardboard above the plastic bars which is tight against the bin walls and then top that with about 30cm of moist bedding material (cardboard, grass clippings and some leaves).
When I transfer two small twin level bin farms would can I feed them straight away if I put the middle trays which is essentially worm casting onto the bedding from both farms and then follow that up with the top levels that contains most of worms or should I wait for a while for them to settle or add some grit or other material before feeding them?
Thanks
 
Roland