TBH, your best bet is first to take a few weeks or months and tinker with already existing mods in order to learn the stuff. For example, in order to have barely decent code writing skills for HW2/HWRM and the most basic competence for working with textured 3D files, it took me two good years of work. So, yep, I would really suggest that you choose any mod out there and try to understand how it does each thing, tinker with it, etc.
Heh, a nice challenge for you that will give you a decent knowledge basis. Take Homeworld 2 Classic and have in a campaign mission your starting fleet include a squadron of TIE Fighter from Star Wars, the Daedalus battlecruiser from Stargate SG-1, the Battlestar Galactica and the Enterprise from Star Trek.
Get them to work on your game and be able to fight the Vaygr units from the campaign and you'll have the initial understanding to start working on your own mod: this is a much simpler and, more importantly, a very defined objective for you to reach first.