In case no-one else is able to answer you questions, here are my 'best feeling' answers to your questions.
you can expect any day at sea to have a more formal evening, than the port days. if there is only one day at sea, then look for any half days in port, as they may use this/these for other more formal nights.
The weather over here has been quite miserable for a couple of months now, so definitely pack some wet weather gear. Temperatures around the UK & Europe are only in the 70's wioth no real sign of change in the next month, so The Baltics will probably be a couple of degrees cooler (especially whilst at sea). However any sun you do get, will be bright & strong, so will cause sun burn on unprepared/unprotected skin.
Hope you have a fantastic time,
Alan & Katrinaq
Last: P&O Oceana December 2016
Next: NCL Jade August 2017
Then: P&O Ventura December 2017
Golden, Grand(2), Caribbean, Royal, Sea(4+1 aborted)
Adonia(4+2), Arcadia, Artemis(2), Aurora(5), Azura(2), Britannia, Oceana(4), Oriana(12), Ventura(2), Victoria(5)
QM2(2), QE2(9), QV(7), QE, Caronia(2),
Oceania Nautica, Minerva, Minerva II, Fred.Olsen(8), NCL Jade, =X= Eclipse, HAL Ryndam, Aza.Journey, CMV Magellan