Setting Up my books for Services rendered this year as tax preparer: Bad Debt not allowed

I am setting up my books for the first time, and I'm super thrilled to do so, but I have so many questions. 1. Bad Debt or fix invoice amount How do I enter in QBO the fact that a client underpay me for tax services? Looks like I'm not suppose to have a bad debt account, so I guess I should just make a note on the invoice and lower the amount charged? 2. Overpayment Looks like I did not have change for a client and he ended up paying me more that I charged him. Same as above question applies. 3. Should I create invoices for every client in QB, or should I just add the bank deposits and enter them in a single transaction? I usually produce the invoice through the tax software. 4. Paypal payments. I received some payments through paypal so I created a paypal type of account but should I just call it cash, or is it okay to call it paypal to know the difference how I got paid? Can somebody tell me what should I add, delete from my chart of accounts. I know is a lot to answer, but if you could help me with a few of these questions would be great! Thank you!