Halo is something that is common with digital projectors and can be helped make less noticeable if you have your screen placed with a black background to avoid light overspill.. It should however not be 'white' but as black as you can get the projector to do... By the sounds of this salesman it may be able to tweak this projector to better black levels...
You can build a Hushbox to help silence and add fans etc... many people here have build complex and beautiful setups like projecting through walls etc... Search for Hushbox and look at some things that have been done...
Screens are as personal a preference as exists in the FP world and will depend entirely on how you setup works, what ambient light you need to fight etc etc... The new trend for digital projectors is grey screens (for the light cannons) but my recommendation would be to build your own (temporarily) using curtain blackout material (vinyl side) for a while this will allow you to experiment with sizing, placement issues, and anything else... You can then order samples of the available screens and see what works without wasting time without the projector and also without spending $$$...
Lastly you seem to have been struck with a common problem when demo'ing FP units that is ignorant salespeople... DO NOT LISTEN OR TRUST ANOTHER WORD THAT MAN SAYS !! If he told you that a DVD was HiDef source or if his belief is that a plain wall is the best screen for the job he doesn't deserve the job.... Trust your eyes (but also be aware he may have equipment in a botched up setup) and ask here for some of the best advice I have ever found online...
Good Luck
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