"Since code is being executed on my server, I want to be extra careful." If you mean security I think your concern isn't necessary, if nothing else you will ha

"Since code is being executed on my server, I want to be extra careful." If you mean security I think your concern isn't necessary, if nothing else you will have less people using your site so whatever issues you do have will take longer to surface. If the concern is performance or loading your backend that may be valid but is also a great problem to have! I would try to get as many people to use it as possible OR at least make the first challenge or two available to anonymous users.