More precise?? OK. I'll try my best.
1. If you check the web
https://www.uscis.gov/i-797-info says "Form I-797 is NOT a form you can fill out..."
3. Just go to the clerk and ask: Can you make me, please, a cashier check? They will ask you what to write on the check, and that's it. (From: PA Name and Case#, payable to U.S. Department of Homeland Security (not "USDHS" or "DHS").
You have everything explained here:
https://www.uscis.gov/forms/paying-immigration-fees
4. There are 2 different addresses depending what kind of delivery courier you use. USPS or any other messenger like FedEx, UPS...
USCIS Chicago Lockbox
For U.S. Postal Service (USPS) deliveries:
USCIS
PO Box 805887
Chicago, IL 60680-4120
For Express mail and courier deliveries:
USCIS
Attn: FBAS
131 South Dearborn - 3rd Floor
Chicago, IL 60603-5517