1. I do think that Game Jams are one of the best ways to improve your GameDev skills, as they allow you to actually finish games and work under a set and unchangeable deadline.
2. I never have had experts to help during a game jam... but I think that might help instead of constantly scrolling through Reddit or Stack overflow for solutions.
3. Browser games definitly do better at a game jam, because they are more accessible. The more polish the better. I find the best thing would be a level-based game with 5-10 levels and a decent amount of polish. If you talk about hosting a game jam, I would like to see ways to make participants think outside the box, like vague themes or constraints that force them to do better.
4. Definitely use the community function to create a team building community so people can join up.
Hope this helps!