Need advice on getting a new tank after few years of not having one.

I has a 45g FOWLR tank a few years ago but had to get rid of it because I had to sell the house and move for work. Now I own a house again and will be set for a few years so I decided I want another tank.

I am going to do a 75g(ish) display tank with a 18g(ish) sump. I plan on starting with LR and live sand but will eventually want to do some coral.
I have never used a sump before so here is where my questions come in:

I plan on getting:
Red Sea Reefer 350 system
EHEIM Compact+ Pump 3000
2 x 150w Heaters

When using a sump do you put the heaters in the sump or DT? I would want them hidden so I dont have to look at them.

Anyone have any recommendation on a good/QUIET in sump protein skimmer? Also any recommendation on lighting is appreciated. I would like programmable LED.

Thanks for any advice