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1) The idea is interesting, but it has several serious flaws.
1.1 - A paid, high-quality streaming channel was introduced; some people bought it, but the quality seems to be the same as the free one now.
1.2 - If you implement a system like most other games, you need to rework some of the Heroes' mechanics. The observer must be in the game because restreaming has several significant drawbacks (delay, desynchronization of 2 streams, quality).
1.3 - Do all the top players have computers that can stream in good quality? It's unlikely that a restream will be that good.
1.4 - Many streamers earn money from advertising on these streams. Try to explore this area (donations + bonus from the stream (contract with Twitch, etc.) and something else), and all of this could generate a decent amount of money.
2) As mentioned above, everything comes down to the duration.
3) The time from 8 PM to 12 AM seems to be the most optimal.
4) I'm not a great player, but I can be a commentator, as I have a good internet connection and a good computer.
5) There are many streaming programs available now, and they are quite easy to set up. For example, Open Broadcaster Software.
Additional idea: What if the commentator explains not the game in progress, but a recording? Then you can properly edit everything, figure out the main points, and possibly include comments from the players themselves – a complete game analysis. This would be both interesting and educational. In other words, make it not just a game with commentary, but a real show