These two covered it very well. Opti-Seal has many uses as A&J has stated. As he mentioned, opti-seal is recommended 1 hour after the last coat of gloss coat to protect gloss coat during the 7 day curing time frame.
You can technically top Gloss Coat with whatever you want. You can wax over it if you wish to. It's just not really needed. But opti-seal, instant detailer and OPT car wax will add slickness to the paint as well as gloss. Gloss Coat like most coatings are not that slick to the touch. They have that plastic/rubbery feel. Heck I have used CarPro Ech2o (QD ratio) over gloss coat with no issues. It sure did leave some nice gloss and slickness after I used it. So feel free to use what you like.
These are the photos I took after an ONR wash and Ech2o QD wipedown. Gloss Coat is coming up at 9 months for me and performing like day one. In these photos Gloss Coat had been on for 6 months.
Same goes for a car shampoo. You can use whichever product you like. Optimum car wash is a very nice car wash. It does have a little bit of polymers as well. Nothing significant. But it does have some of the frothiest suds of any wash I have used. I have used Meguiar's Hyper Wash and CarPro Reset as well and they do not alter the performance of gloss coat. ONR for me is just so convenient to use on a weekly basis that I rarely bucket wash these days. Part of that was because of the drought here in Southern California which forced me to go rinseless/waterless.
As far as a waterless wash, I am not a fan of ONR in that regard. Feels a bit grabby for me. Same when used as a quick detailer. Instant detailer feels much better when it comes to a quick detailer due to the slickness left behind. Opti-Clean is a waterless wash and feels better than ONR as a waterless wash. Give ONR a try as a waterless wash and see if you like it. If not you always have opti-clean as an option.
OPT car wax is really optional. The one reason to have it in your arsenal is when it comes to decontaminate gloss coat using the wash, clay, wax method. It's also fresh paint safe so if you happen to have a repaint you can use it safely. I have it in my arsenal.
But I would recommend investing in ferrex for not only prepping the paint but also for when it comes to decontaminating the paint coating down the road.
Anyway no need to overthink it. Experiment and have fun