How do i decide on the cost of a player
Do it manually, do it based on popularity, or do it based on a single stat (average acs in role seems to be the best option, here)
if I make the website live for each champions tour event, how do I deal with teams being knocked out?
If this is regarding automatically updating standings when matches happen, you'd have to use webscraping.
If this is about the points allocation, I imagine you'd just use the stats from the games they played to allocate points. If they're out they'll no longer give the user any points.
Do i only allow a certain number of players on a team per role
Up to you. Limiting the players per role leads to more diversity in fantasy teams, leaving it unlimited may lead to more participation due to increased familiarity with the players.
Regarding stats, you can either scrape VLR.gg or use the RIB.gg analytics bot in their discord : https://discord.gg/aceNhaM . The latter is probably better, but some stuff needs a premium subscription. However I don't think you'll need one for this project
GL dude