Your tank deminsions sound fine, close to about 150 I'd say. My only suggestion would be to have a sand bed depth of at least 6" if you want to run DSB. From what I have seen, and researched there are considerable issues with a sand bed depth between 2" and 6". Mainly releasing phosphates and Nitrites. That being said, there are quite a few people running systems that are not "rule of thumb" with no issues, so you may end up being okay.
Those dimensions are for a 125, not a 150.
I think with a good ATS matching his system he wouldn't have problems with a 4" sandbed, especially with a decent CuC. I agree, tho, a remote DSB might be better, and cheaper!
I don't think a tank would look weird like that, a lot of people (like myself) are huge fans of the shallower tanks.