I don't have any pokes, but I'm pretty fascinated by them. If you can, post a photo of your cage when you get it built and let us know how you constructed it. If you have a positive experience with the set up, I may follow suit.
Most people I've heard don't do screening though, as it might be easier to just to drill holes on the outside. I would say, 3 rows of evenly spaced holes (well, maybe an inch apart?) all the way around the enclosure, with a few holes in the top for added ventilation. But the size sounds great! And if you do do the screening, that sounds fine. Pokes don't need a lot of humidity, they are considered Medium humidity species. So you have a lot of room for error.