Use Вы and you never make a mistake.

As for me.
If my interlocutor is older than me i use Вы. With age-mates i prefer Ты. 

This winter is pretty warm in Moscow.
The average temperature is about -10C as usual. The coldest days were  -20C. 
So there is nothing dangerous at all) But we had more colder winters.

Поразмыслить/обдумывать - equal to each other. But the first verb has a perfective aspect and means the result. The second verb has an imperfective aspect and means the process. 

Усесться - perfective aspect, means the result.
1. to sit comfortably.
2. Another meaning is to do something in sitting position. For example, to read a book (усесться за книгу) or to drink tea (усесться пить чай). 

Подсесть - perfective aspect, means the result.
1. To sit near someone.
Also this verb has figurative meanings:
2. Get tired. (устать)
3. Hooked. For example, hooked on drugs (подсесть на наркотики).

Прояснить/уяснить - I agree with Aud and alex.

Заведение/учреждение - I agree with alex.

Зодчество/архитектура - I agree with Aud and alex.
Also архитектура has two meanings:
1. Style of building, architectural style. Дом современной архитектуры (The house has a modern architectural style).
2. Generalizing meaning, means buildings at all. The architecture of Moscow is very diverse (Архитектура Москвы очень разнообразна)

I left any attempts to find a language partner.
It didn't come to my mind that the number of learners is more than the number of native speakers. But i found several non-native speakers and we had nice conversations. It wasn't a language exchange, because we just talked in English and none of my partners were interested in learning Russian. Only one guy corrected my mistakes and i'm grateful to him. So i don't see any sense in conversation for conversation, when you make mistakes and nobody corrects you. I can improve my active vocabulary by keeping a diary or by visiting an English speaking club in my city. But i want to speak like native speakers and here i need their help.
Another thing is a language exchange. But there is particular case of what i told before - the number of English learners is much more than the number of native speakers learning Russian. And here all depends on the level. I saw many topics here where people with an elementary level are looking for a language partner, but honestly they have to find a good teacher, courses or to get  at least an intermediate level by their own. English is a very simple language for learning, to my mind. But Russian is the really Hell, especially for foreigners. I can explain some things and rules, but if my partner doesn't know anything in Russian it's like a conversation with an alien. 
So today i'm not looking for anyone (btw need to renew my profile). It's hard for the reasons above. I learn rules, do exercises, google things that i don't know, keep a diary, write messages here, watch TV series, listen to music, try to check my sentences for mistakes and I'm fine. Of course, i make mistakes (even here i made some), but this is a way too to get a knowledge. So i became an autodidact.

Certainly, I don't like to look at the departed, because the death is an ugly thing. But sometimes you need to do that.
There are no strict rules about that in Russia. If you don't want to come to the funeral, so don't come.