for a projection surface buy a polyester tablecloth on amazon, they work great for front and rear projection and are dirt cheap and more durable than bed sheets (also cheaper). they do hold creases but if they're loosely folded or rolled up it's not a big issue, or toss em in a dryer for ten minutes on low and it'll come out.

Don't put your projector where anyone can spill their drink on it, knock it over, or steal it.

And a cheap AV switch box makes it much easier to plug a bunch of different things into your projector.

I dress my band in all white.

Once I stacked up a bunch of guitar and bass cabs and put white fabric over the grill cloth.

If you have a decent projector and a dark enough venue I feel like you don't really need a screen just point the projector at the stage and let you/your band be the screen. White flat bed sheets also work but I think tyvek type material would probably work pretty good as well and be much more durable. And if you use sheets I would recommend bringing an iron and a towel(to use as an ironing board) with you to iron out any wrinkles from transporting the screen. Projecting on 3D objects is also pretty cool for live shows. I've seen people preject onto weater balloons and it looked awesome.

I'm looking for suggestions and do/do-nots for building screens for visuals.  My plan at the moment is to make a frame out of 1 1/2" pvc and stretch some white tarp material over it.  I'm aiming for 4'x8' of projection surface on a 4' stand.  Sound reasonable for a decent sized bar venue?