I bought it about a year ago and immediately put it in a larger pot. (I've learned the lesson though). It's been doing OK but recently leaves have been wilting and some of them turned yellow. I don't water it more or less than before so I don't understand. Maybe I should fertilize it? It's in the corner of a north and an east facing window. Nothing is worse than loosing your money tree!

To be frank, I think it looks perfectly healthy. Even a healthy tree will occasionally drop a leaf or two.
But did you move it recently, or is it exposed to cold drafts?

That is one older leaf at the bottom of the plant. The rest of the plant looks great.

DON'T fertilize now. DO be careful with the water.

Why not fertilize?

I've cut 2 yellow and dying leaves from it already. It does get some draft from the windows. Also when I go to work I turn off the heat so there is some diference in room temperature between day and night.
I'm thinking of moving it to a smaller pot.

IMHO, this is not the time of year for the plant to grow much, so it doesn't need food. If the plant isn't using the food, something else can, IE rot organisms.

I care for plants at my workplace. One I inherited was a pothos in a much, much too big pot. With weekly small waterings though. it has done tremendously well. My guess is that with LIMITED water, there is always enough soil mass to soak it down away from the roots. Point of the story, it might be happier to stay in the same pot as long as you are letting the soil dry enough between waterings.

To me your plant looks okay. I just saw a friend's similar plant and it is in much worse condition.

I agree with the suggestions, do not fertilize right now, and try to keep it warm. I always delay or not do fertilizing during the cold season, plants are slowing down naturally. Just resume it if you really need to during mid Spring and be mindful of watering during these cold months, plants are not consuming much with the colder temps and decreased natural light. I would also delay repotting if you really have to in mid Spring.

OK I'll be careful with watering and won't fertilize.
The labels that come with plants usually say things like "fertilize every two months" or so. I've never followed them!

Is this black spot on the leaf normal or is it some kind of disease?

The pot is very large and that makes inadvertent over watering more likely. Overpotted plants tend to put more of their energy into filling the pot with roots at the expense of top growth. So, be patient.

Fertilizer is not medicine and is intended for use only on plants that are healthy and growing vigorously. Plants use nutrients in very minute quantities and not at all when they are not growing or growing very slowly. Manufacturers want you to buy and use a lot of it so they promote its over use.