Hi @csurname,
Glad you reached out! The Salesforce add-on is a purchased add-on, and we can’t support that here in the forum. Your best bet for getting support for those types of add-ons is by reaching to us at givewp.com/priority-support/
In the meantime, I’ll help as much as I can here.
First, yes, you can create Recurring Donations with Salesforce (we include mapping information in that documentation you linked above).
At the moment the integration doesn’t support custom objects, donations are strictly mapped as Opportunities. We do have documentation for sending custom data that might be helpful: https://givewp.com/documentation/add-ons/salesforce/sending-custom-data-to-salesforce/
And I’ve also created a feature request for this here: https://feedback.givewp.com/feature-requests/p/custom-objects-in-salesforce. You can use this link to follow our progress or provide additional details. I’ve also linked this ticket so we can reach back out to you with a resolution.
I’ll need to mark this as resolved for now, but if you have other questions we’d be happy to help over at givewp.com/priority-support/
Have a great day!