i'll answer what i can. i would use the cover , given you have a clear cover, anytime you are not using the pool. a clear cover will absorb the solar energy by day and transfer into the pool at night..obviously, watch for algae bloom as if you have it on too long, it will have a greenhouse effect..i've only had my cover about a week (blue) and haven't left it on at this point more than a day.

in terms of the reel, what i did to allow me to evenly pull the cover off is attached 2 ez grabbits (about 5 inch long plastic bar grommets that don't damage the cover..then attached a rope to each. i put the ropes to the side of the pool before unrolling then go to the far end, grab them both and slowly pull the cover into the pool. it's working great! my pool is 18 x28 and so i can imagine with your 20 x 40..it's not as simply as gravity and a little bit of current going to pull that cover into the pool. if i don't use this system, the cover just sits by the reel until i help it along..if you search ez-grabbit online or check at like a home hardware/camping store, they should be easy to find..there is also a guy on ebay.com, mike from colorado..really nice guy who sells these for a good price in a 4 pack. matter of fact, cheaper than i was able to buy them at my local canadian tire store by a dollar or so.

in terms of leaves, etc on cover..the common tip is to use a hose to blow them into your skimmer if you have one on top while the pump is running..in my case, it's a 2 minute cleanup with the net to get them off so i just do it that way.