I have a tiny garage and built an enclosure around my SO3 that is about as wide/deep as your model: at times you will wish you had more access on the sides (e.g. maintenance, checking V-wheels), BUT mostly this is fine (and me, I had no choice anyway, that’s all the width I had). Height on the other hand…don’t make that mistake many, many of us did. Build it MUCH taller than you think you need, because of all the reasons mentioned previously, and because if quietness matters to you chances are you will eventually upgrade to a watercooled spindle, which means cooling hoses coming from the top of the spindle. Having to dive into a tight enclosure to check something in the back of the X rail, well I have been there, it’s no fun.
For the vac cooling, ideally you will want to design a baffle/muffler as Will said. Here’s a random pic from the interwebs that illustrates the interesting part: making sure the air has to zigzag to enter the enclosure
(no air outake in the enclosure itself in this pic, but you get the idea)
I went with poor/lazy man’s solution, cut a hole in the bottom right of my enclosure near the ground, cut another hole on the top left of the vacuum compartment, attached kitchen air extractor to that hole, wire the extractor to the same plug that activates the vac.