(1) A loan is a loan. The fact that in this unusual case the loan may be forgiven, forgiveness does not occur until it has been given. Incoming funds would be treated as quite simply a loan payable. We do recommend setting up a new general ledger (GL) account in your current liability section for "PPP loan" for each company that you receive these funds. It makes absolutely no difference, for accounting purposes, whether you receive those funds into an existing account or into a new account: it is still a loan payable and the only question is which GL asset account it affects (i.e. increases). Even as the funds are being used for the intended purposes, no accounting entries would apply that are different than normal. Just as if you received a loan from a bank to buy a piece of equipment, the loan payable account doesn't change until/unless you make repayments of the loan. Only when the loan is actually formally forgiven (which requires a special application to be completed) and you know precisely whether some or all will be forgiven should the loan account be adjusted (see #5).
(2) Continue to process payroll, rent and other expenses in the same way that you always have. You don't start to suddenly process these somehow differently than before. You don't, nor should you, pay these out of a separate account. If the PPP funds physically exist in a separate account, you would transfer funds from that account to your regular account for rent or gross payroll (not including payroll taxes that are solely paid by the company) but the only accounting entry involved is decreasing one cash/checking GL account and increasing another. (In Advanced Accounting, GL-L Transfer Bank Accounts Funds accomplishes that very easily.)
(3) Keep separate track of what you use the PPP funds for outside of your accounting system or use a method, such as job cost codes, that have no accounting impact. Do not try to convolute good accounting practices to try to account for how the funds are used to meet IRS tax requirements. Most users will be best off using a spreadsheet program for this purpose. Or, in Advanced Accounting, users could use the job cost module to keep track of funds used for PPP purposes, which can be used in an integrated or non-integrated manner and tied to transactions that do not otherwise impact your overall general ledger. In this regard, you could set up PPP "job" with certain tasks (payroll, rent) under it or use different job codes for different PPP expense types, the sole purpose of which would be to generate reports later for complete the forgiveness form and for monitoring purposes to ensure compliance.
(4) Generally accepted accounting practices often differ from tax handling practices. Do not offset your payroll, rent or other accounts based on how PPP funds may be applied to meet loan criteria. Your expenses are your expenses. For tax purposes, your tax return preparer can net those off against expenses if that's what the IRS continues to decide they want; you just need to make sure that the funds are used for the applicable expenses and within the applicable time limits (the percentage and number of weeks have since changed from that they were, so keep in touch with your tax adviser in that regard).
(5) If the loan is forgiven, write-off the loan in full or in part to an Other Income account in your books (on that future date when it is officially forgiven). Tax handling aside, don't sacrifice you accounting system for the whims of tax requirements, even though your accounting system will still have all of the details that your tax accountant will ultimately need. Generally accepted accounting principles would require that you recognize a forgiven loan as "other income." The IRS instead does not want it to be included in income but instead offset to expenses. But again, good accounting practices are not the same as tax accounting requirements. Your books should accurately reflect your financial position and follow accepted accounting practices.