Recently I went to bank & representative told about various offers available

They were - increase credit card limit, overdraft protection & Unsecured line of Credit

Since I may need Unsecured LOC soon, I inquired more details
I am pre-approved for $10000
Interest will be Prime plus 3.65

Is that Usual rate of interest for Unsecured LOC or its it too high ?

They told me about offer expiring by end of this month

Also as per bank rate of interest as well pre-approved amount will change next month

What critera they use to detemine Unsecured LOC ?
I am suppose to take Unsecured LOC only with bank where account is OR
I am allowed to take from any bank

How usually payments calculated in Unsecured LOC ?

Thanks