I am trying to make a banking mod for the sims 4.

Planned Features:
Savings Account - accessible by computer or phone (ability to open account or close account)
Interest - 2% base, with ability to haggle for higher rates (eventually)
-Interest added weekly on Sunday
Ability to Deposit and Withdrawal money
Auto-Deposit from paycheck - *multiple percentages*

So far, I have finished most of the XML menus and can easily inject them into the game. The roadblock is the functions/python scripts attached to these buttons.

Recently, I have completed nearly every tutorial for XML tuning and have tried to learn how Python modding works. However, I still have a few questions:
1. I assume the t in XML t="" is type, but where is the list of these?
2. How would I calculate the interest weekly in xml or python? I plan to use an object in the sims inventory to hold the balance of their account but how do I add the 2% to it weekly? Basically, I don't know how to make a script mod do this weekly without a command input or how xml can do this.
3. Is there an index or explanation for all the python files? Its overwhelming right now as I am trying to learn.