On the particulates......this is just a fwiw.
When I made my screen, I wrapped the rigid screen in regular fiberglass screen ( the replacement stuff on the roll ). I did a lousey job in that the fine screen material ended up having alot of folds in it on both sideas of the rigid stuff. Ya know I do find a good bit of dirt particles in it when I clean out the leafs & junk.
I was actually kicking around the thought of using the HVAC filter material that you can buy in the HDW store/ Home Depot. It looks like fiberglass matt as the fibers are randomly oriented...it's plastic fibers not fiberglass. Usually the stuff is used in air handlers at the "exhanger" location as a particulate filter. There is very little or no resistance to flow across this material. I just can't figure a way to make it easily changed out.
Tom