I've decided to do Iron Man. Since all of the issues are available, except for the last 15 issues of Tales of Suspense. And after Iron Man I'll read another character.
Like, since the 30s? That's gonna be a huge list. Just pick a place to start, say, after the Siege event, and go from there. And then go and read older stories if you want. Don't overthink things.
'Sigh' Maybe it'll be if I start from the beginning of the Modern Age of Comics. That's the 2000's right?
Seriously. Just pick a spot and start, for crissakes. If you miss something, it'll either not matter to the story, or it will, and you can go back and read the issues. You are not performing brain surgery here.
I'm persnickety this way. I should just start with Marvel NOW! and go from there. The app comes with a getting started section with various events and series.
Here is a site I have been using for a reading order and tracking my reading. Its great because you can customize your own comic box, get virtual badges for your reading progress and lets you know if its on Marvel unlimited as well. It has an order for marvel 616, marvel from the 30s and ultimate universe. It's a reading order based on publication date and chronology, emphasizing publication date, not chronology. So you won't find titles like untold tales of spiderman at the beginning on the order. You can always use other info for that. It's a really cool site that I would recommend. Complete Marvel Comics Reading Order | Marvel Comics in Order
If anything, I'd focus on past big events. I started reading with AVX and All New X-Men. I eventually started reading some back issues/events on stuff I was interested in. If they bring something up from the past, I'd just google it and see exactly what they were referring to if it really bothered/interested me.