What goes on at JW wedding ceremonies? Are they that much different from other Christian weddings?
Naw. People are excited about the bride and bridegroom; there's usually a reception; everybody is hooping it up; some folks have a little (or a lot) too much to drink; everybody goes home happy.
And what about funerals, for that matter?
Perhaps a little bit different. No wakes, or "periods of silence" for the departed. Very very rarely there will be a graveside ceremony. I was a pall-bearer once (when I was a teenager!) for good old Eddie. It was a simple matter of transporting his casket to the hole in the ground; nothing was said.
At what age are young people considered to be first able to decide whether they get baptised or not?
Depends. For many years, it was simply a matter if you could "prove" your worthiness to get baptized (I was baptized when I was 10). Then, the WTS 'tightened up' on the parameters, and it tended to move more toward being at least in the mid-teens.
Are JWs obliged to throw away/burn birthday and Christmas cards and presents that get given to them by unknowing non-JWs?
Not explicitly, but it's "understood" that one should dispose of such artifacts.
I have heard conflicting things about what is supposed to happen to people other religions when The End arrives. What exactly IS supposed to happen to those not in 'the truth'?
Again, it depends. In the "old days," anyone who wasn't a JW at Armageddon would certifiably die the death of Gehenna. They've shifted somewhat from that position, to "only God knows."