For the NHL team idea, yeah if you want a serious league as Pengwin suggested it's probably not the way to go. However, perhaps a second league with the same group of managers that might work. It gives everyone one 'serious' league where you try to build the best team possible, and other more 'casual' one so you can be more of a fan of specific teams/players.

Also in multiple category formats, depends on what type of activity you are looking for. If you like smack talking and competing against one another, then go for a H2H league. Though in this one you have to accept a bit of luck as in the playoffs anything can happen. Or if you prefer a marathon and one where every stat counts, then roto is the one for you. This league usually ensures the best manager winning.

For league depth, I think your suggestion is a good one, as it ensures that the teams are deep enough but there are still options on FA to keep everyone active. You could even increase it to 4 starting per forward position with 6 starting D, but that comes down to preference.

I don't have experience in keeper leagues so cannot give you feedback there.

But regardless, as Shakedown suggested, it depends on whether you already have a group of managers to bounce ideas off of, or whether you are starting from scratch, which could be set up with your preferred settings and then recruit like-minded managers.

Good luck.

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