really?? that's funny because the threads i found on other forums, autopia i think, had a 5SS rep saying it can be layered with any wax?? Maybe you're getting confused with the fact you can't layer 5SS itself?
What i was referring to before about resprays and carnauba's is that a fresh respray needs to cure/breathe. A carnauba can do this, a sealant (like 5SS) can't. BUT ~2-3 months after the fresh paint, feel free to do whatever.
You can go just straight sealant, or sealant and wax, or just wax.
Depends how fussy you are with swirls/scratches, but some products contain fillers of sorts. Whilst not really desirable as they mute the metallic a bit, products like Zaino's Z5 can help with light swirls/scratches, whilst giving you shine and protection.
Best bet would be get it professional done once off, so they'll clay, polish, etc. If you're going to do 5SS, either ask them to do it, or just ask them to detail the car, but not use any LSP (last step product). That way, they give the car back to you, and you can try the 5SS steps.
You environment sounds pretty harsh, so for a black car that seems to be getting some harsh treatment from the locals, definitely go with a sealant first. Give 5SS a shot, and then i reckon layer a shit load of something on top. I'd still go OCW for it's ease of use and cheapness. So after applying 5SS, you can then after every wash after, layer some OCW ontop and get maybe a good 4-5 layers going. Should be ample protection for you car.