I'm by no means an expert on projecting a picture, but having had to install one in my bedroom, a few thoughts crossed my mind.
More important is that it should be 90 degrees to the wall for ultimate accuracy, if you're not going to use keystone correction.
If you think about it, the floor could be level and the wall on the p@ss or vice-versa.
Also important I would think, is Yaw. In other words, the distance from the screen to the left and right front face of the PJ itself.
Explanation of Yaw below, as I'm not sure I've made that clear;
Flight dynamics - Wikipedia, the free encyclopedia
In fact, seeing as you mentioned airfreight, perhaps that link is quite relevant and the 3 pics demonstrate all the things you should bear in mind

But I digress.
That said, perhaps I worried about it too much, in which case I'll be interested to hear what more experienced users say
I don't have a clue re: your second question, sorry.