Stockholm questions - ferries vs tours; itinerary vs loose, day trips?

We all want to see the city from the water. Should we hire a tour guide or join a tour to see this? What do we miss if we just use ferries to get around some instead?

Either works. You really don’t need a guide as it is mostly about the scenery. Keep in mind that the ferries are mostly about getting from point to point, so take the ferry if you are planning on visiting a particular island. There are some archipelago tours focusing on the inner part of the archipelago that are geared towards tourists; they will cost more but they may be a more efficient use of your time. Check the Stromma website for these.

Do we have enough time to do a day trip to Sigtuna or somewhere or is there plenty to see in the city and surrounding area?

There is plenty to do in Stockholm, but you have time to take a daytrip if that interests you. If you decide to do a daytrip, I’d probably choose Uppsala over Sigtuna. There is a lot more to do in Uppsala.

thank you!

For seeing the city from the water, I'd suggest doing both: use the local ferries for travel and a dedicated boat tour for a proper guided experience. For your itinerary, a loose schedule is fine, but I'd still buy tickets in advance for popular spots like the Vasa Museum to save time. With your short trip, there's more than enough to see in Stockholm without a day trip. You can spend that time exploring the city and doing some proper fika, a great way to experience Swedish culture. You can find some great spots for it on fikastockholm.com.