Hi @PJMcD, hope you are doing well!
Regarding the activities, it seems that they are known in SF as tasks, and can be synced with HubSpot as described here.
On the other hand, at this time we do not currently sync with Salesforce notes.
A workaround that is an option is exporting the notes from Salesforce and then importing them into HubSpot as you already know. For notes, this article goes over properties that can be imported for notes.
You can see an example import file on this article, just to provide a visual of how the file should be setup!
For example, you can download the “Companies and notes sample spreadsheet” to see the columns being used for the notes. This example import is associating that note to the company. If you were wanting to associate it to the contact, you would replace the company information with the contact information (i.e. First Name, Last Name, Email, etc).
Hope this helps clarifiy,
Diana