I am new also and am working on billing and contract issues. I am planning to have an hourly rate and three monthly packages. Each package will include a discount off my hourly rate based on the number of hours.
I was thinking of doing two separate contracts -- one for my hourly clients and one for my monthly retainer clients.
The billing and contract issues (as well as finding the right theme for my website) have been the most time consuming items in starting up my business. Once I have these squared away, I will feel much better.
Good luck