8 weeks - summer/fall of 2022

I like the idea of using your Marriott points for a big city visit. When I retired a few years ago we used all my Marriott Points for a week in Paris. We even got upgraded to a suite and took advantage of the Conceirge Lounge for drinks and meals.

I’ve been to the 3 cities you mention but on a cruise so didn’t go outside of the city. Loved both Copenhagen and Stockholm. I would probably choose Copenhagen for more things to see in the city.

Enjoy.

You're smart to try to use the hotel points in costly cities.

I'd take a look at September and October weather statistics for the Scandinavian countries before making a final decision. Norway's actually the most expensive--I think by a considerable margin. Five nights in Oslo might be a bit much, considering all the other great places to see in that country (starting with Bergen and the fjords).

I think five nights in Helsinki is almost certainly overkill. I'm looking forward to going (it was to be part of my 2020 trip), but I don't think it needs five nights. And I'm the person who spent 10 nights in Barcelona and 10+12+14 nights in London (on three different trips).

I'm planning on more time in Stockholm and Copenhagen.

I would choose Stockholm over Copenhagen.

If you are going to Helsinki, you can take the train to St, Petersburg, Russia. Check if short term tourist visa may be available with hotel package. Maybe they cooperate with Marriot? Remember that winter starts early in Scandinavia. Leaves were turning when I was there in August. Spain/Portugal/Italy all sound good for October. Some friends of mine went to Norway a couple of years ago and said it was expensive but they enjoyed cruising up the fiords and Fiordland National Park.

I would choose Copenhagen hands down. Very easy to make day trips and lots to see. I love it spent 8 days. I purchased a Copenhagen card which I found great value for me. I know everyone does not there money's work from these cards but I did.

The visa-avoidance strategy for St. Petersburg involves an overnight ferry from Helsinki. It's an intriguing option, though again I'm iffy about the weather that late in the year. (I was cold in St. Petersburg--then Leningrad--in August 1972, but that was before climate change.) Moby St. Peter Line runs the ferries. You spend a night on the ferry headed toward St. Petersburg, two nights in a hotel in the city, and another night on the ferry as you return to Helsinki. So you get two full days and big chunks of two other days in St. Petersburg. And you avoid the major, time-consuming hassle of trying to get a Russian visa. I think those visas cost over $250, too.

I'm considering taking advantage of this no-visa loophole when I finally get to make my trip(s) to that part of Europe, but I have not done so yet and cannot vouch for any aspect of the experience.