I'm not so sure that desk will hold your tank
But seriously, that's a great lookin' setup so far.
You, IMO, will need more in tank flow than the 3 powerheads you have now, but I'd be inclined to leak test everything first and see how you like it before you buy more.
As far as the tiling goes, I'm the wrong guy to answer it for you, but I do know it's doable as long as it's done right. Otherwise you'll destroy the tiles.
I'm not familiar with your skimmer, but many are over-rated, although some are close. You'll probably end up with around 160g DT plus your sump, so you'll just have to try it and see. It's a good brand, but I know not of it.
Some tips;
-fasten your PVC to the stand to alleviate stress on the glass
-use flexible or 'spaflex' hose where you can to alleviate stress and vibrations
-if your sump is not already baffled, plan it well, then think about it for days. Then plan it again. Many of us wish we had thought it through more our first go 'round
-some members have used 'rare earth' magnets to hold the stand skin on. Works great as far as I have seen
And I'd highly recommend you leak test everything with tap water. Completely fill everything to where it will be and let it sit/run for a day or more. That's a lot of RO water to waste if you have issues
