Just so you know, if you choose Trondheim, then it is about 14 hours drive to Lofoten, and that's the "boring", inland E6 route. There's a more scenic, coastal route, but that will add a lot more driving time and also more ferries. Beautiful drive, but little time for Lofoten.

Another two options from Tromsø:
If you want to fly to Tromsø, then you also could take the passenger catamaran to Harstad, (3 hrs, 7 AM and 4PM). Might save some money, but probably not time.

The scenic way is Hurtigruten coastal steamer overnight from Tromsø to f. eks Stokmarknes. Leaves Monday, Wedensday, Thursday, Saturday and Sunday night from Tromsø and arrives in the Lofoten Islands in the afternoon. About $200 per person, but you also cover a night's sleep.

If this was my trip, I would fly to Tromsø, drive to Lofoten, and then spend the last days on the "outer way" north to Tromsø. I think the Senja island would give you good impressions on fjords (smaller scale, but equally impressive than driving out from Bergen). I would stop at Husøya, and plan some hikes. You can get impressive views and experiences just by short hikes. And there's the very slight chance of seeing the northern lights.