Cash Method and write off's

[Martijn Heuts]

Hello,
Can I use the 'Cash' method for bookkeeping with GNU Cash?
I have a medical office and often insurances pay 4-6 weeks from my invoice date.Therefor my revenue on P&L shows really good, so does my profit, yet I didn't make this profit.
When medical insurances pay me, they only pay me like 1/4 of the invoice (6 weeks later).What is the best way of dealing with:
* Write off's - When a medical insurance pays me a fraction of the invoice, I put everything else as discount so the patient ends up with a 0 balance. Is this the right way of doing so or is there a better way?
* Reporting - I print out my reports every month, yet in the next month I receive money from the medical insurance, at that time i discount the invoice to 0 after applying the insurance payment amount. This throws the revenue report off for the month the invoice was placed. Should I just reprint every report at the end of the year so everything matches, or is there a better way of dealing with this?

My last question comes from a profit stand point.According to the P&L report I made a certain amount of profit. However of this profit amount I am paying a business loan which is not an expense (besides the interest). When I file my taxes how does this business loan come into play?Say that it shows I have 10k profit but I paid 8k in business loan, for me personally that means i only have 2 K net profit, yet the IRS is going to charge me taxes on the 10K?
Thanks for helping me understand.
Have a great day!!
Martijn