let me put it bluntly, there's no "simple" way that someone with no knowledge of FS2 data structure or modding would be able to do without massively ****ing up.
you copy paste the stuff you want together -> the required models, textures, effects, tables
then you have to make missions to put them all together.
good luck, have fun. though you probably won't have fun. Mashing mods together is pretty damned boring as you need to make sure you didn't miss some crap like an effect, or a table. Speak nothing of balancing. having ships just shoot each other really gets boring after a few minutes, and putting the whole thing together takes time in the magnitude of hours. In the end, you'll just have a bunch of ships you can ctrl-click in FRED...
If you want to have any sort of objective based play you're going to have to write that yourself...and at that point you might as well polish it and release it...
Every newbie wants to mash together a megamod. I'm rather thankful that in FS2, it isn't easy unless you know how to build a mod yourself (and in that case why aren't you?), and the result is utterly disappointing.

Man, I've modded games where this was somewhat easy, and hot damn man, there were all these mishmash megamods, and
by god they SUCKED.
Don't let this discourage you from starting a serious mod/campaign though. That's a worthwhile effort.
Random mishmash for personal amusement?
Probably not worth it. You won't get too much amusement out of it (at least, I don't, and I make campaigns not because I like to bask in the e-fame, but because I find it genuinely fun. Copy-pasting fifty different files into the correct folder/plaintext file? Boring.)
TL;DRDon't bother.
It's a lot of work, and I bet you the result won't be as fun as you think it would be.
Make a real mod/campaign instead!