Custom Transaction Type uploads

We have multiple external billing systems that do not integrate directly with NetSuite. At the end of each month we will post the necessary entries to recognize revenue, billing, etc. During the month cash receipts from credit cards will be posted to NetSuite manually. The number of transactions can get quite large. I want to create a template which will allow us to download from our various credit card processors, automatically manipulate the information in excel, and upload the information into NetSuite.

I am playing with the design of this in our sandbox. To more easily track this I have created a custom transaction type called "credit card deposit". I set it up as a "journal" transaction style (it can go to multiple bank accounts depending on the situation). For document numbers I set up a prefix of "CrdCard" and told it to begin with an initial number of "1". I set it up so that administrators and Accountant/AR/AP profiles have "Full" permissions.