I have only ever flown this route in J (business), but some relatives fly this route a few times a year in Y so I should have an idea...

Q1 - dinner following departure from SIN and breakfast before arrival in HEL (around 2h before arrival) - I would assume typical economy class meals...

Q2 - yes, lights are off

Well, not sure if I would worry about thermals...

...and I would not be overly worried about the connection. Just did something similar via HEL last week, and the whole process only took a few minutes. It will be quiet at security and immigration (arriving from Asia) at 6am in any case.

If the plane is late (unlikely given that it normally stays in Singapore for 7h or so), there are later flights to Berlin during the day. I do get stressed travelling in third world countries, but would not be particularly concerned about Singapore or Helsinki airports...

Safe travels!