Do we have to record something in the general ledgers when a business submits a quote to supply their stock (sale)?
And how do we formally balance revenue/expense/OE accounts in the general ledger? (Do we use the same process of balancing Assets/Liability accounts?)
A quote is not a transaction, so we do not record anything.
To answer your second question, revenue and expense accounts are 'closed' to the profit and loss summary account. They are not balanced because revenue and expense accounts are not carried over to the next reporting period. Keep in mind that our revenues and expenses must be relevant to the CURRENT reporting period.
It is probably a bit difficult to explain this process here, but if you're using the Cambridge textbook, you'll find it in chapter 9. But for now, you shouldn't worry about it too much, you'll learn it near the end of unit 3