I bought a new fly from SLO several years ago. Vents N/S and one window/one vent E/W on each side. Works well. Typically, I don't find that a lot of ventilation is needed when the fly is on. I think just two N/S would be plenty, and windows on all four openings E/W would be desirable.
I use a combination of bungees and straps.
The biggest issue for me with the SLO fly was needing to seal the seems. It was challenging to lay everything out so the seams were flat and get it sealed properly. I used SeamGrip and did two coats on the inside only. Never had a leak.