Hi cleanspace,
It looks like you've got some good suggestions here from Fiat Lux. I like that you've using the QuickBooks Community to get ideas of other services you can use from users who may have similar businesses to yours. I'd be happy to shed more light on QuickBooks Payments for QuickBooks Online.
QuickBooks Payments works based on an average monthly volume, meaning that the program will allow you to process a certain amount of funds without them being flagged and help. This monthly volume is chosen by you, and you should be able to set a high limit amount so that you can process large payments like you've described. You can learn more about QuickBooks Payments from the links below to see if it's a good fit for you.
QuickBooks Payments doesn't have an insurance option that you can offer to your customers, but I can see why that would be important given the amount of funds you'll be working with. If that's something you'd prefer to be built into the payments processor, I recommend researching other options to see if there's something else that can meet your needs. In addition to ones mentioned above, you can also learn which payments processors connect with QuickBooks Online by visiting the Apps tab and using keywords to search.
I hope that helps you with your decision. I'll be here if you've got more questions. :)
