as Ozzfest05 pointed out, you can mount the PSU at the top by removing the top 230mm fan, and have 2 x 120 at the bottom and maybe add one at the top.

As for dust, it doesn't have dust filters, but as of now, it seems good on my side, but I had it for a too short time to tell. Honestly, I'd say it's better than the Nine Hundred and easier to clean too. Honestly, it shouldn't be a big issue in that case.