Looking great! I like the open space in the upper part of the tank. Gives the fish some wiggle room, and they'll appreciate that.
I started with a 29gal+15sump. My current tank. Moving to a 125+55sump + 40breeder (frag tank?) soon. A 65 is a decent sized tank. I have 4 fish in my 29 (pretty much maxed out). African Midas Blenny (awesome fish), 2x Clowns, and a Six Line Wrasse (don't get one without reading up on them a lot LOL).
Once the tank is cycled and ready, you are good to add your first corals. I started with frogspawn, hammer, and paly's. Mostly photosynthetic and they don't kick up the bioload really. As you got your liverock and sand live, you'd probably be in the clear (I'd think) to put in two fish to start. Yes, definitely get a decent skimmer. Go for one rated for a tank size notably larger than your system. I use a hang on back Remora (not the pro model) on my system. Though it is rated for a larger water volume, I find it just keeps up. But it could do better. My 125gal upgrade includes an ETSS skimmer rated for up to 400 gallons. I can't wait to see that sucker in action.
About your sump. Liverock is always good. The more the better I say. I skipped putting sand in my sump however. Some people do it. Some don't. I found sand unnecessary. My key parameters are on the mark. Nitrates and phosphates at 0, etc. But... I am rock heavy. I probably have 80lbs+ in my little system. Consider adding chaeto to the sump and putting a light over it (assuming there is enough water volume in there). If you put it on a reverse night/day schedule it'll help steady your PH, and help remove nitrates. Agreed on the bioballs. No need for them. The filter material is fine. Some use that. Some put a sock on the overflow outlet. Others don't filter it. At the moment I don't have a filter on my sump.
If you go with a hang on back skimmer for the display, make sure it has a surface skimmer. If the skimmer goes in the sump then not required. You could consider putting a skimmer outside of the stand if you are tight on space. Feed the skimmer with a pump in the sump. It runs outside the stand to a skimmer, which then feeds back into the sump return. The potential problem with that is noise and/or not wanting to see a skimmer in the living room. For safety, the skimmer should have something below it to catch a potential skimmer overflow.
Lots of possibilities and options. Its what keeps us on our toes, and our wallets empty.