Roles:
Main Duelist: this role gets bonus points for first bloods
Flex: this role gets bonus points for KPR
Inititiator: this role gets bonus points for ADR
Controller: this role gets bonus points for APR
Sentinel: this role gets bonus points for clutches
You could also steal Prtsy's idea of them having to play that role but that gets complicated as viper would have to classify as both a controller and sentinel and for teams like liquid your just fucked as they all seem to play every role, so personally I wouldn't go for this but you could.
Pricing:
I dont know if you can but if you make a stat like this guy (https://www.youtube.com/watch?v=7QCR19qYPgI) then you could use this to value the player but it would be harder for new players.
Another method is to put them at what you think they should be for this season and their price goes up and down going into the next seasons based on how much they were bought compared to the average plyer and new players are just manually added at a level you think they sould be.
Eliminated Teams:
Group stages are easy as no one is eliminated until the end for playoffs you could just have it be part of the challenge picking winning teams but to make it easier allow subs so that if main member are knocked out if you have lets say one sub for each role the substitute is put in for the rest of the tournament.
Overall asignment of points:
One option is to use a stat like the one I mentioned before and use a multiplier to trun it into points.
Another option is to do something simple like ACS or KDA as they are not affected by the special bonus points for each role:
Alternative:
If you steal Prtsy's idea fopr an average across a tournament it fixes the playoffs issue as well as the liquid issue for roles.