First solo travel - Lithuania & Latvia. Advice?

Hello everyone! I am planning my first solo travel (F25) for the end of August this year.

Since it's my first solo travel, I have a few questions for people who have been to both these countries.

At first I was thinking about spending a few days in Lithuania, 3 in Vilnius (plus a day trip in Trakai) then take a day trip to the spa in Druskininkai. After that, I was thinking of spending maybe 2 days in the Spit National Park and then head to Latvia (Riga) after stopping to see the Hill of Crosses on the way there.

When it comes to Riga, I was thinking of spending 2-3 days there as well and a day trip to Sigulda. Maybe also visit Jūrmala?

All in all, I am wondering if my itinerary is too packed or not enough. Also, I would need advice on how and where to meet people and fellow travelers, since it's my first time travelling solo.
One more thing, are there any hikes organized to also include foreigners/English speakers? I would love to also explore the nature there.

Any information is welcomed!!! Thank you :)