Congratulations on your new tank. It can be a lot of (meticulous) work to set up, especially if you are OCD like me LOL.
Here's some suggestions and what I'd think about doing. There's a lot of info about where and what to buy, but you will want to get an idea of what you want to do for YOUR situation. We can go on and on in much more detail in anyone of these topics, but this is just some ideas. Based on what you decide, my suggestion would be go deeper into understanding what you'll need to do in more detail. This is just what I'd do, there's probably about a thousand variations.
Dual overflow and Drain:
* I don't think you need to buy "kit" for the drains. Buy needed bulkheads and PVC for the holes in the overflow. I would set it up as a HERBIE. That is, each overflow will have a full siphon drain, and a secondary trickle/emergency drain. For the full siphon drains, add a strainer to block any larger objects. With dual overflows, it can be challenging to dial in, but I know many folks on here have this set-up and it works great was dialed in. The trick will be to drain both overflows back to where you have the filer socks in the sump.
Sump:
Mechanical: I'm a fan of filer socks and I'd go with that for mechanical especially since you already have holders in the sump. It looks to be easy maintenance too,
Bio: It appears the bio-balls would be fully submerged and not a trickle filter based on the pictures. IMO, that's not a problem as bio-balls would still work. BUT, if that were me, I would get marine pure balls or blocks or any of the dozens of other options for submerged media. I would put in that chamber. Or you could just put the bio filtration in the larger chamber and that should be good too - do both if you want. i would just ditch the small chamber with bio-balls, if you do it right it's not needed. It doesn't hurt, but I don't think you need it. Hard to tell from the picture, but you could use that for some polishing pads.
Heater/Return PUMP: Put heaters in the sump. Essentially there are the titanium heaters will you need a separate controller OR ones with their own thermostat, BUT you'll want to also include a separate controller for redundancy. Many on here prefer DC pumps. Off the top of my head I think of about 8 DC pump brands. DC pumps will allow you to control the outflow without the need of ball valves. With the return pump, The volume and size of pump will be based on how much turnover you want for your tank. You'll want to think about how you want to run the return plumbing BACK INTO the TANK. the easiest way without additional holes would be to go over the wall and in the tank directly.
I have used stand alone UV, but not inline. Honestly, you may not need this and unless you plan to doing inline with your plumbing, I would just hold off on this for now and prioritize other things above. Oh, I personally do not use chemical filtration of any kind of carbon for operation. IMO, you don't need it. Others may have varying opinions so may have more ideas for you there IF you want to go that way.
Hopefully, this offers a few ideas for you to think through ; - )