Post it in the beta board so that (hopefully) people can test it and check that it works, maybe make a few suggestions, etc., etc.. You know the routine, at least in principle.
The beta testing board is very flexible: you may post there anything that vaguely looks like a mission or part thereof.
When finished, a mission template should be submitted to the Editors Depot. Please include a detailed readme with information on what the prefab contains and how to use it.
Addons are irrelevant to this process, although of course it is
very strongly recommended that you use only addons that have an official
OFP TAG. And of course you must give precise and accurage urls.
But most importantly, it's great that you want to give something back to the community. :thumbsup: