You seem to be asking a mix of Bookkeeping, Tax Basis, Financial Management, and Best Practices. These need to be examined separately.

Bookkeeping = track everything you know about. Your idea to connect banking is the wrong perspective; that is when the Bank processed something and not your client's perspective. If I pay you in Nov, and you cash it in Jan, we have different tax year reporting perspectives, and cash vs accrual does not even apply here. I spent the funds when I paid you, in Nov. The Banking will show it for when you finally submit it to your bank, if I sent a paper check. And for Credit Card use, the date your checking account pays the credit card balance is not the date there was an Expense. It's the date a Debt Balance was paid; that isn't the date you bought things using that credit card.

Tax Basis = reporting it to State and Fed and other agencies per the right perspective.

Financial Management = track and report and evaluate everything. An accrual or a cash basis entity needs to run reports on both perspectives. Example: my governmental entities that are accrual basis might look like operations are great on accrual basis reporting, but cash basis reporting shows cash flow has significant delays or bottlenecks. You can bill out $5,000 for the last date of the month, but that Accrual Basis sales won't show on Cash Basis, until the customers start to pay.

Best Practices = you will want to enter everything you know, and need to help the client understand their financial reporting, to understand their own operations and activities for them to manage their business and be successful.

This is a rather odd statement: "For accrual basis with inventory, I haven't really gotten an answer for that."

Then I recommend you establish a relationship with a CPA. Get one that will be your own consultant, so that you have a resource for learning what applies. Even as the tax rules change or are refined, this person does something you don't also have the time to do = stays current with the applicability of how to implement the data tracking to meet these requirements. And when you work with clients, you will also work with their CPA, to make sure you are helping the client you have in common meet the expectation of their own CPA.

"Although my understanding is if they generate less than $25 million, then they can choose to use the cash method, which will be most of our clients"

Inventory is an Asset, so that is value still on hand. A Cash Basis entity has to modify their reporting to be able to account for the value not actually "spent" but invested in their inventory.

You will want to spend an hour or two reviewing these basics with your own CPA, as a continuing ed process. Then, consult with them any time you get a client that has something different than what you already learned, so that your understanding continues to grow. That makes you more valuable to all of your clients and to potential clients.

And the QB Community is at this other link: https://quickbooks.intuit.com/community