If there is a platinum series, then it includes Price of Loyalty. I think it will be possible to find a version that would suit everyone.
The deadline, as I think, is at least 4 weeks.
Dates... for example, 04/15 - 05/15.
Thus, by 04/14, it will be necessary to:
-) decide on the format;
-) decide on the tournament hosts and judges;
-) prepare tasks for the tournament;
-) formulate the rules as clearly as possible.
The version is not a problem at all. You can Download the entire game in about 5 hours.
But it is better not to delay the start of the tournament. The number of participants will still be 5-6 people, since there are only a few who know what Heroes 2 is.
It is better to play offline, since Heroes 2 crashes too often online, and I don't know why...
And the rules can be taken from the League of Heroes or other sites; they were developed over many years, and there is no need to invent anything new.
Everything else is up to the moderator of this topic.