I set up the self-hosting option, but doesn't look like you can OAuth into any of your accounts, and all balances/transactions have to be managed manually, is that right?
Yeah I agree with this. Dedicate 1 to 2 hours of focused work, fill it out, and move on.
This assumes that you're far enough along in the sales process that there's a high likelihood of close (you've already negotiated price and timeline), and the deal value should generally be five figures or above. This means it's worth your time.
Slightly risky hack: you can buy yourself some additional time by answering some questions with "Documentation will provided separately", and often times clients don't follow up to ask for it.