Renewing parts for Giants Revel 0

I'm the proud owner of a Giant Revel 0. I have got it for around 1.5 year. I has gone through summer and winter, rough conditions. In the time i haven't renewed any parts or did much for the bike (shame on me!).

But by now i can fell its not running as smooth as it did when i bought it. Gear shifting, chain, brakes (can push it all to the stear), and tyres seems to be getting wear.

As i'm rather rookie, i don't have the sligthest clue about what to buy if i should renew parts. I have been reading several articles, but can't seems to find specific brands that are 'good', and what to look for when buying etc. brakes, cassettes or something.

So i thought maybe you guys could help me? What would be a start when the bike is 1.5 year? I'm defiantly thinking about a new chain, and need some tyres that can resist snow and ice (winter conditions in Denmark atm.) - should i renew cables?
If any Giant Revel 0 owners out there, i would also like to hear what your thoughts are!

Hoping to get some help!