My thoughts. Whether you go 16:9 or 4:3 realize that the native resolution of the projector is important. I'd still pick a 1920x1080 1080p projector in preference of any other consumer option because the prime concern is pixel density. Most 720p projectors are actually 800p 1280x800, Most 4:3 projectors are 1024x768. Your 1080p projector is 1920x1080. I might be going a bit remedial in all of this but the important thing in all of that is the 768, 800 or 1080. The 1080 in that 1920x1080 means that you have 1080 lines of pixels for your screen vs 768 or 800. Any projector can do 4:3, 16:10 or 16:9 aspect ratio. I would just use a 1080p projector with 4:3 resolution. Both AMD and Nvidia drivers handle setting it in slightly different ways but you can do 1440x1080 4:3 on a Optoma GT1080 or BenQ W1080ST.
15% overlap is good. It's right at what you need. It's always ok to go over that with larger overlap. THe edge blending won't work right if you go less though.
At issue with Nvidia 3D vision is there are a very strict limitations Nvidia has on it. It has to be a certified projector in order for the driver to register it as something that can be used. Sometimes people will hack the EDID to make Nvidia think a non-certified projector is certified, but it's a three ringed circus to get that working correctly. Often times you'll have the wear the glasses upsidedown on hacked setups.
Often times I'm right on top of posting, but looking at the forums it doesn't really give others a chance to chime in on topics. I'm experimenting a bit with the idea of waiting a day or so before replies to see if that'll get the community to post more. Not sure it'll work, but I'm experimenting a bit. My main goal of hte forums is an open flow of ideas. That's not happening when I always chime in.
I used Carl's Place material on most of my early 2010/2011 projects. It's a PVC plastic material. At issue is getting it to lay properly on the screen curvature without ripples or bunching. I found my ultimate solution with that particular material is to put a run of adhesive velcro along the top edge and have the sides and bottom free floating. That way there is no potential for bunching or rippling of the material because it's free hanging instead of affixed on all sides. The problem with affixing it on all sides is that it must be perfectly flat and there be no flex in the circular screen frame in order for that to work perfectly. There is no such thing as a perfectly flat or perfectly rigid circular screen frame, so it never works out right if all sides are affixed. It's best to leave it top hanging and let the sides and bottom be free hanging.
He can do as big as you'll ever need. Just realize that while his material works, affixing it to the frame is an issue you'll have to work though. This isn't like stretching the material to a flat frame. Stretching material to a curved frame introduces some unique problems. A forward bow towards the screen radius centerpoint or bunching and rippling if applied unevenly to the frame. His screen material will work ok, but you're going to need to do some problem solving in relation to how it's affixed.
Back when I got his material he didn't have the gray material options yet. I'm curious how the gray PVC is vs the white for contrast. I'm thinking the gray might be better for circular screen application, but it's only a guess on my part. Someone will have to make the first leap and do an experiment on it.