Tsugirai: Hmm, maybe I should give H1 another try... However it kinda bothers me that all 4 factions have the same missions but only one of them are canon. H2 at least has some different missions. Also playing the same town through the whole campaign gets boring fast.
You are taking the role of a commander for one of four competing rulers. As I understand it, you'll play the same maps regardless of your choice of sovereign (with one exception) because all four sovereigns are competing for the same territory. Only your starting location will be different (except maybe in the maps where you conquer each ruler). For example, the sovereign you chose to follow determines where you start in the first two maps, but the map itself isn't fundamentally different.
There are a series of four maps where you conquer each sovereign in turn. In a given run of the campaign, you won't play the map featuring the conquest of whichever ruler you chose (so if you chose to follow Ironfist, you won't play the "Conquer Ironfist" map).
Tsugirai: I will play Chronicles for the story no matter what, I actually love story based games even if they have little to no actual gameplay, I just thought maybe I should play the games in order of difficulty instead of order of release, to keep it more interesting and have that ramping up challenge.
Sadly, the story bits in Chronicles dribble out a little too slowly for my liking. A lot of them show up at the beginning of a specific turn number, so there are story segments that you might not see if you are too fast. The story is still coherent from map to map, just be aware that you don't need to rush.
Storywise, you can mostly play Chronicles whenever, but generally play them in order since some of the later ones reference some events from earlier ones. For HoMM3, make sure to play Restoration of Erathia (base campaigns) before Armageddon's Blade (first expansion).
The connections between MM 6/7 and HoMM3/4 are much more tenuous. The two game series are very different genres, so NWC made sure the story generally made sense without having to dip into the other series. The references are a nice bonus for those who've played both series, but you will still be able to follow the action even if you don't hit Might and Magic 6/7 before moving on to HoMM 3/Chronicles.
Tsugirai: Yeah, I want to play through them all, even 7 (I heard that's really bad but I wanna do it nevertheless)
I assume you mean HoMM7, as opposed to MM7? Because MM7 is great.