There are a few extra data fields that we need to store for our customers. (booleans for ‘open support case’ and ‘non-standard pricing’, customer number, permanent payment reference number, preferred invoicing method (snail mail / e-mail), and real estate id)
The way I see it, the best way to implement this would be to extend the party model. Is that the sanest option? Also, has anyone done parts of what we need? Especially the customer number seems like something other people might’ve needed as well.
Yes, this is the recomendend option. For the customer number, if you unset the party sequence on Party configuration you will be able to manually enter a code for each party. Then you can store the customer number there.
For payment reference number, the account_payment_sepa module adds the sepa creditor identifier to the parties, maybe you can also use it (or take a look on it in order to know how to extend the party identifier to add cutsom codes).