well your question was answered properly above, a thank you would suffice, next time elaborate a bit better...
well it is up to you really? I normally offer the player double his current value, but players like Messi, Ronaldo etc you need to offer at least 150% of their current value, even 200%
also depends on your clubs status, I sold Erdinc to Man Utd for £19.5m when he was only vauled at £6.5m!
I would not sell Messi though