- How to play Heroes 3 online.

so, regarding the versions:
RoE 1.0 and 1.1
AB 2.0 and 2.1
SoD 3.0, 3.1, and 3.2

Dix Bukovsky: parts 1, 2, and 3

this is most likely the Platinum Edition (disc 1 contains HMM1 & HMM2, discs 2 and 3 contain HMM3)
currently, people are playing SoD 3.2 and 4.0 (this is the Platinum Edition)
regarding the connection - the game uses TCP/IP (you can also use IPX, but Hamachi doesn't seem to support this protocol). To connect, you need Hamachi (a virtual network that assigns an IP address), or you can use an external IP address if you have one.
regarding the traffic, I can't say for sure, but 15 MB is the maximum (the initial map + movement on the map, I think even 5-10 MB is enough).