I have been told that you can not bring over NOTES.
I do not know what Maximizer 12 is. If it is a database centered app then i’m sure you can export all the data, accounts or whatever. Then with something like MS access or LibreOffice Base you can sanitize the data. By sanitize I mean clean the data up to have the smoothest transition to suiteCRM. Then simply use the import function in the admin section of suiteCRM. Map the fields to each other and import. All your data will then be nicely imported for the crm. As far as event, task, and things of that matter I do not know how you can import those. But for your “notes” you could always have it dump into a textarea custom field. For my crm migration I simply had a field labeled “Old CRM Notes” and dumped the data onto there. Although I was only using the other crm temporarily and did not have too much data to begin with.