PieSync supported syncing Microsoft Business Central. You can keep using PieSync through 2021, but in the meantime we're checking if we need to prioritize turning this into a data sync app? Please upvote! Thanks.
In 2023 we'll look to release an invoice sync for Business Central. To note: those invoices will likely just sync to a dedicated 'invoices' object inside of HubSpot, which in turn you can associate to won deals (but you don't have to)... Basically what data sync would do is make sure you can have those invoices live in HubSpot as the very thing that they represent (= invoices) so that these records can trigger automations and fuel reporting in the very way you want them to.
Double clicking on your need of what you'd get out of BC items actually syncing into the HS product library... I understand it will make quoting a bit easier! Good to hear that.
As to your note on customer sync: you're very right, and it's an issue we need to deal with on a level beyond just Business Central, and in fact beyond data sync in general. The very ambiguity of customers representing both B2C and B2B is what causes a disconnect a lot of our accounting syncs.