Manual/Offline/Cash Payment option

I'm trying to start a simple membership record for a group. The group is small but handling the registration manually is a mess.

I don't plan to use online payment at least not this time, so it's only Cash payment, The user can enter the page, either login directly or register.

On registration, the new member will be assigned as "Payment Pending", on which the user should pay by cash, The admin will manually activate the account.

I would like to keep everything else, mainly account expiration period and expiration email notification to both the member and the admin.

If a member logged in he will be directly redirected to the summary of his member ship, especially the expiration date.

So basically, I just want to add a cash payment method, where the user can register directly without any payment, and should be assigned as Pending Payment status by default. The admin thus will manually add the payment for each. But in the same time I want to retain the Membership features (Expiration date, expiration email notification, etc..).