First year of auction style keeper league

[bisklimpkit]

With the fantasy trade deadline looming I'm trying to get our league to nail down the rules for keepers for next season, as I think it may affect what happens in trades. What are some standard rules for keepers that we should incorporate? We are using ESPN, and currently have it set to allow 3 keepers. I'd like to see a premium paid for a keeper (% of $ paid last year, or just an arbitrary number?) and also limit a keeper to a 3 year term. Thoughts?
Also wondering about trades in the off-season. Is this something worth considering? Does anyone know if it's possible to 'buy' a player from someone, so that you could trade them a player in exchange for more money to spend in next year's auction?
Any other popular rules that we should be thinking about?
Thanks!