I use solution listed above with zerotier for android and linux as network solution for private connection. I was also doing reverse proxy for zm but later I resigned in favour of static ips and direct connections (due to unrelated to zm issues but I remember configuration not being straightforward in case of reverse proxy)

Zmninja last I heard isn’t developed anymore but should still be working.

Cameras with exposed rtsp are best for this solution. Do you need wireless or wired? What cameras you have?

I am not sure if a week will be enough to troubleshoot luxurious things like access over domain (unless you have experience :) ) but if simplified enough it can be all set up pretty quickly.

I am available for further help if above scenario is followed.