Hello pam0315, 

Thanks for joining us again here in the Community. I can further help and add up to the detailed response given by my colleague, @AldrinS. 

QuickBooks Desktop is great for allowing users to manage transactions and accounts based on their preferences. The set up would depend on how you want to track your finances, and I can guide you through it.

You can opt to mark all expenses as billable from the Preferences page. Anyway, you’ll have the option to assign a customer or remove the checkmark in the billable column when you create bills (see screenshot below).

Yes! To easily track the mark-ups of the billable expenses in the Profit and Loss report, it needs to be an income account. It’s money in type of transactions though!

Once you mark a bill as billable, the program automatically recognizes it as reimbursement from client. Therefore, regardless of whether you choose to use the reimbursable or any other expense accounts, your customers would need to pay you back.

The choice is yours; you can continuously use the Temporary Power or Facilities, or a new reimbursable expense account. All you need to do is create an invoice for them, so they can process the payment. I’ve added a screenshot below for visual reference.

In connection to your fourth question, if you want to create an income account specifically for the mark-up amounts for better tracking, you may do so. I’ve added steps below on how to do it:

1. Go to Lists at the top menu bar, select Chart of Accounts.
2. Right-click and choose New.
3. Select Income or Expense in the Categorize money your business earns or spends section.
4. Choose the other necessary details, click Continue
5. Enter the Account name, Description, and etc.
6. Click Save and Close.

Then, for the last question, I’d suggest consulting an accountant to verify if there’s a need to link them with the Cost of Goods Sold account. They are the experts with tax and account-related concerns to ensure accuracy of your books come tax time. 

You can now proceed and enjoy working with your account. But, if there's anything else you need help with, I'm only a comment away. The Community is always here to help, anytime!