I ended up using the unique numbers on the salesforce entities (Accounts and Opps) and created the lookup fields (columns) in the dataverse pointing to them on the parent record. I added a couple subgrid's on my accounts, one on two different tabs showing only related too opps. and imported my opps separated by the record type (our two different job types) in the Power Query Import so the existed as separate tables in the dataverse. This also ensures my users are creating the correct type of opportunities for the accounts moving forward, since they create new opps from these same Subgrids.
I was never able to get all of our appointments to sync to opps in import, finding this to be due to countless user errors over the years in salesforce relating appts to accounts or not relating them at all if they made them from the wrong entity, so it was not always that one entity from salesforce that the lookup field on the dataverse was looking for, causing the import to always fail. Instead I added the lookup field on the appointments and elected to import the related unique id and put it on the appointment form right by the lookup so it can be referenced in cases of service work, when past appointments need to be references in the dataverse search. The user can than link the appointment to the opp manually as they work through things as they come up naturally. Luckily the dataverse search, if configured correctly, makes finding things easy on the user side.
The import of data was the most stressful, grinding wheels aspect of my power apps experience, i had to do it many times with it failing before i could get it to take.
ALSO, important step that is easy to overlook, your opportunities will fail if they dont have a parent account, so always make sure your account important is done first and that nobody is creating new accounts and opps while you are doing the import. So if your accounts are importing, and by the time you are importing opps, someone has added a new account and opp in salesforce (the account being missed from the account import) your opportunity import will fail, since it will be pointing to an account record in the lookup field that does not exist in the dataverse.