I feel you on the gigantic idea, but the reality is that as a single human you are absolutely constrained by time (i.e. your healthy life span) and there isn't a way around that. Your only options are a) write the story as a web fiction (significantly faster than drawing), b) make it your full-time job so that you can devote full time hours to making the comic and work at a pace where you can finish the story before you die or c) get a well-paying job in an unrelated field and hire a full-time professional to do the drawing for you.
There are a TON of short cuts you can take to reduce time per page (which have been detailed elsewhere), but even with those tricks, you would still need to spend hours per page, which circles us back to the sentence above. There aren't really short cuts to long stories.
Personally, I went with option A while I work on shorter projects and build publisher connections, then maybe in like a decade I would have the necessary health and options to dive into the longer story (if I still want to, that is. I'm quite enjoying writing single books right now).