1) sheep rarely lasting 20 min is probably good. i'd even argue that sheep never reaching the time-limit is ideal (*practically no ties/always a clear winner, *rounds/fun don't suddently stop, especially for the sheep, *wolves don't get a free pass by slacking until the round ends if time-limit is increase or removed entirely, etc). one good reason to keep a time-limit is to avoid 2 hour rounds with unfair teams. just make sure that the wolves get exponentially stronger to keep an acceptable average survivalrate. why exactly do you want sheep to reach the maximum time-limit alot? or even at all?
2) 2-20 was always exaggerated and was never a real problem (the notion that rounds can last short/long instead of averaging around 10 minutes, with 1-2 minutes deviation). this has been covered before. kind of crazy to propose a decrease in the 2-20 scenario, yet argue that we need more 20 minute rounds? or am i missing something? usually people wanna decrease 2-20 by implementing a more centered spread of survivalrates, where vast majority of games fall somewhere within 7-13 minutes.
3) st is a game where both teams play both wolf and sheep. it's not a "sheep vs wolves" game in the sense that you only achieve balance/good map design if both sides win equally much. such a fallacy was used before as support to remove the stack-farm, because it made the sheep "have an unfair advantage". complete garbadge.
anyway i wish u the best of luck, shoop and chakra are a great team for this project (one theory king and one technical king).
edit - nice theory: increase isolation-power from wolves and escape-power from sheep. get rid of the anti-stack-stomp and anti-stack-mid. the counter to more escapes/saves from sheep should be more isolations/kills from the wolves. the choice to limit the use of the stack-farm makes no sense to me, when the reason stack was added is because it singlehandedly adds more fun to the game than all other farms combined. there are other ways to counter it/''balance it out"(as demonstrated by the stack in older versions), try figuring something out. stacks seem poorly incorporated in current ST based on streams i've seen, and is the biggest reason i cba play st anymore.