This, dear friends, is Howto 2: How to turn a bunch of awesome levels into an actual campaign!
OK, so you have a few levels, but if someone were to actually play you mod, all the levels would be available with all their missions and they'd have no idea which to click, and you want it to be like the original campagn was with all that nice progression stuff.
Well, it is within your grasp! Having had to do it about 4 or so times now, I've kinda gotten used to it. It is however, a rather odd, and out of order process, which is for all intents and purposes, quite hard to describe.
This How to is less of a how to, and more of a guide, that is, you kind of need to read it all to know how to get along ok, rather than go through it step by step to make your mod a campaign.
And lo, the difficult 2nd album begins...