Adding Existing Clients to new WHMCS - to be invoiced 1st of month

Can someone advise if I am doing this correctly as I have spent hours reading/testing WHMCS products/services and don't know if my setup is the best way to do this.

We are manually adding all our existing clients into WHMCS and have picked 1/6/17 as the first date for WHMCS to start invoicing these clients.

Our clients purchase monthly recurring services from us that are invoiced on the 1st of every month, eg. on June 1st, their invoice will be rental from 1/6/17 - 30/6/17.

I have Prorata Billing enabled, Prorata Date set as 1.

Charge Next Month is currently set as 0 as these are existing clients (I'll change this to 20 after June 1st so it only applies to new clients)

After I add the client, I add the product & select Do not generate invoice/Do not email.

I then edit that Product so that both the Registration & Next Due Dates are 1/6/17.

I also edit the First Payment Amt to take out the prorata portion; ie. so it is now the same as the Recurring Amt.

Will this mean that on the 1st of June, it will generate an invoice for 1/6/17 - 30/6/17? (I have disabled Invoice Generation as I don't need invoices sent out prior to the 1st of the month)

If that's what it'll do, then great; mission accomplished! However, is there a simpler way to achieve the same thing?

And I haven't even started on how to add charges to said 1st of month invoices for excess usage that I have to bill for manually! But I'll save that for my next post!

To anyone who can help/advise: my sanity thanks you!