Hi there, danielk1.
Thanks for reaching out to the QuickBooks Community. Let me help share some insights about the multi-currency in QuickBooks Desktop.
I appreciate the detailed information you've provided. QuickBooks cannot generate the exact conversion in advance since the rate is subject to change. Once you post a USD entry for a specific transaction, it will be recorded at a rate of 1:1 or the last entered rate.
To answer your first question, the option is, you'll need to change the As Of Date and Exchange Rate manually so QuickBooks automatically grab the FX rate at the start of a day (attached screenshot).
For your second question, you can use the home currency adjustments this will calculated based on the difference between the exchange rate recorded with each transaction and the exchange rate as of the home currency adjustment.
It's calculated on:
Lastly, there isn't an option to update the FX rates by batch for a certain period. Instead, you'll need to change it manually.
For additional reference, you can check this article: Set up and use Multi-currency.
If you need further assistance with the process, I encourage you to contact our QuickBooks Desktop Support Team. They have additional tools to pull up your account and do a screen-share.
Here's how you can contact our customer support:
Please know that you're always welcome to post if you have additional questions about the Multi-Currency. Wishing you and your business continued success.