Stayman for Four: Transfers for more!
There are no lower point limits for using Transfers. You just need five of a major suit.
Why use Transfers rather than Weakness Takeout?
Because both Partners gain the opportunity to bid again(if they wish) and the stronger hand remains Declarer.
Stayman may be used whenever the response helps your hand!
Normally you would have 11+ HCP but if any reply by Opener improves your bid then use Stayman!