Baltic and Scandinavia itinerary - help needed.

I will spend nearly three weeks in the Baltic and Scandinavia. I have been to Stockhom and Helsiniki but none of the other cities I will travel to on this upcoming trip. Here's my rough itinerary,I'd like to know if i have allocated the correct number of days to each city.

Day 1, Arrive Vilnius - arrive in the am, could be tired from the long flight.
Day 2, Vilnius
Day 3, Vilnius
Day 4, early am train to Minsk
Day 5, (sunday) Minsk - day trip to MIR castle
Day 6, early am train to Vilnius
Day 7, bus Vilnius to Riga
Day 8, Riga
Day 9, Riga
Day 10, Riga
Day 11, Ferry Riga to Stockholm
Day 12 (sunday), arrive in the morning to Stockholm
Day 13, Stockholm
Day 14, ferry Stockholm to Tallin
Day 15, arrive in the morning to Tallin
Day 16, Tallin
Day 17, Tallin to Helsinki by ferry
Day 18, Helsinki
Day 19 (sunday) Depart Helsinki

My questions.......

Am I better off leaving for Helsinki late on day 16 instead of on day 17. I get the impression Tallin is very small and can be seen in a day, and the city is dangerous at night. The hotel prices in Tallin and Helsinki aren't much different, and I would like to visit sights in Helsinki where I'd been years ago (Sibelius Monument and the Rock Church in particular)

What are the best companies to use for buses between Vilnius and Riga?

Do I have too long in Riga? Any day trips recommended from Riga, I don't want to visit the beach, prefer cultural and historic sights.

I think most things will be closed on Sunday, so I've marked which days are Sundays in the itinerary.

What changes should I make to the number of days I've assigned in each city? I need to start booking my hotels, so I need to be certain I have the correct number of days in each place.

Any advice is appreciated, thanks.