The group stage of the World Championship for Heroes of Might and Magic IV is currently underway and will last for another 2 weeks (until April 14th), so finding players who are actively playing the 4th installment online right now might be a bit challenging!
Also, not many people can play equally well in all the series, which means the number of potential participants will be even smaller!
But in principle, the idea is interesting, although quite complex! If you can create a set of rules and make the tournament engaging, post it and see if you can find willing participants!
Personally, I can offer assistance with Heroes of Might and Magic IV; unfortunately, I can't help you with the other series!