Husband (83) and I (63) are just back from our 14 day trip to Scandinavia. We had a great time visiting the different countries and after 10 months of planning, I would say it was a success. Used the RS Scandinavia book as a template and that worked out fine. 3 nights in Helsinki, 3 nights in Tallinn, overnight ferry Helsinki to Stockholm followed hours later with express train from Stockholm to Oslo for 3 nights there, then 2 nights in Aurland (had a rental EV for this leg of the trip) and final night at OSL.
We managed all this with a backpack (35 liter Allpa for husb, 45 liter REI for me) and LLBean boat tote bag each. I packed clothes in large ziplock bags and sat on them to compress the items down and that helped greatly. Neither back pack looked "full" to capacity and fit just fine in the overhead bins. The totes went under the seat in front of us.
I booked airfare last December- economy with refundable option and I did pick seats. Used my United miles to get from our hometown airport to O'Hare, then SAS to HEL and back from OSL with a stop in Copenhagen each way. At the time of booking, this was the most economical option. A friend recommended stupid looking waffle inflatable seat cushions and OMG- did they ever work out wonderfully! Inflate 1/2 way only when cruising altitude is reached. They deflated easily and were about the size of a deck of cards folded back up.
Lodging all made through booking.com- free cancellation and breakfast included. Yes, I used the hotels in the RS book... We are farmers so having a larger breakfast is our normal. Speaking of food, we will often stop for lunch or a late afternoon snack and we rarely have "supper" unless we missed lunch. On the trip we ate supper 4x. We went on the trip to see the sights and museums, did not go for a gastronomic experience of fine dining. If we wanted a beer in the evenings, we picked these up from a local convenience store.
Only in Oslo did I get us a 48 hr city card for museums and transport both. In Helsinki we just got a 24 hr transportation pass so we could go to both the open air museum and the fortress island on the same day. For the trip up to the narrow fjords area we had a rental car and I was brave and chose an EV without prior experience.
For "connectivity" I added the international plan on my USCellular phone (plan already removed) and that did well enough. Estonia was a bit "iffy" signal-wise but the locals told me that was not uncommon, esp. in the Old Town. Hotel wifi was good and fast everywhere.
Since the trip was pretty much "refundable" I only added a travel health-only insurance policy for the two of us as "you never know."
The one splurge of the trip was hiring Mati Rumessen for a 1/2 tour in Tallinn; was fantastic. Weather was sparkling and he is a most excellent guide and driver.