If you do a lot of work, You will have to deal with the dust. A DC system collects sawdust as well as the dust. I fill two 55 gal barrels a week, don't think I would like all that piled up around the shop. Fresh sawdust will kill grass.
As for the ducting, the main reason it is overhead, is because we need the wall space for shelves, storage, etc. I ran mine at 4 foot as much as I could. When I researched mine, I was told to use 6" but I chose 4" because I wanted to use 4" PVC. (with a grd wire)
Cut it twice, and it's still too short!