Need Urgent help with leaves and white fungus

Hello, i'v had this bonsai for 2 Months now, im suprised that it still lives but im not happy how i'v taken care of it.
The weather has gotten colder and colder here, last i checked, it was 10c in Estonia, plus its always raining, so no sun, barely any warm air.So i'v left the bonsai near a window, so it wont get blasted by cold air constantly, but i'v noticed that some green leaves have fallen off, is that due to Cold air?
Also, there are some leaves with spots on them, someone told that it comes from under/over feeding it.
There are some pictures of the trunk, you may see white fungus growing on it, you may also see some rutes out of the soil,what causes this?OH!And pruning!I made various pictures of it,is it time to prune it?How do i do it?
And, a month back, someone told me "That is a chinese elm tree in bad soil", so i ask you, would it be VERY bad if i repot it in a few days?

https://2img.net/h/i226.photobucket.com/albums/dd12/demon4777/IMG20110811_001.jpg
https://2img.net/h/i226.photobucket.com/albums/dd12/demon4777/IMG20110920_004.jpg
https://2img.net/h/i226.photobucket.com/albums/dd12/demon4777/IMG20110811_003.jpg
https://2img.net/h/i226.photobucket.com/albums/dd12/demon4777/IMG20110920_006.jpg
https://2img.net/h/i226.photobucket.com/albums/dd12/demon4777/IMG20110920_007.jpg
https://2img.net/h/i226.photobucket.com/albums/dd12/demon4777/IMG20110920_008.jpg

Your tree is quite chlorotic, but other than that, it looks healthy enough.

At this time of year, leaves start to get spots. They're ending their useful lives, and even if they don't fall off (as with some elms) they will be functioning quite poorly.

I saw nothing wrong with the roots.

You can eliminate the chlorosis problem by using a balanced (NPK) fertilizer with a full complement of trace (minor) elements -- manganese, iron, magnesium,, etc.