often thought about such things as i occasionally use projectors at work (in live music enviroment- tho they are usually higher rated projectors)
One thing i would bring up is bulb life- manufacturers figures are often somewhat misleading
- bulbs tend to develop a green 'cast' during the 2nd half of there 'expected lifetime' and often at different rates which would be somewhat noticeable in a multi projector setup.
I would budget to replace at 1500-2000 hrs as a set of bulbs of matched manufacturer/batch (maybe 2-3000 hrs in eco mode)
Lens offset- the projector you list has quite a high offset which may cause some problems in setup in portrait mode. I'm sure you have the physical side worked out to get a 'virtual point of projection' but i'd be slightly concerned at getting a perfect match up with the most 'distorted edge (the normal 'top') being next to the least distorted ('bottom') of the next projector.
This is a 'theoretical' problem and you should be able to compensate with keystoneing - but it is something that would nag at me if i was spending 5k and i would certainly look for other options with less lens offset if going portrait mode if possible.
That's my thoughts anyway, be very interested to see how it goes
