Its pretty tough to say whats important to other people. We don't do camping and on our 40 footer we have all the comforts of home.
There are some 32 footers with lots of space for one person and some others that would feel cramped over a weekend. Get out and see as many different boats as you can. Go to the liveaboard harbours and talk to people who are doing it.
A few things off the top.... look for a boat that can be easily insulated. Most liner built boats are very difficult if not impossible to insulate so look for a stick built boat (one with conventional floor members and plywood bulkheads as these are easier to insulate).
What amenities on board are important are up to you but a water heater is a must. Of equal importance to whats on board are the facilities of the place you keep the boat....is some method of winter pump out available ? is there a method of filling your water tanks when the harbour is frozen over ? How far is it to the washrooms and showers for when your holding tank is full and you run out of water in the middle of a winter storm.
Keep in mind that this is not an inexpensive way of living and a small apartment is likely cheaper.
If this is truly what you want to do its a great life, go for it.
Dirt People Scare me