Before You Begin.

The first issue you must contend with is what you need versus what you can stand to live in!  I think that a good idea would be to empty your kitchen and perhaps dining room or other attached room and live in it for a week or perhaps two.  See if you can perform all your activities without accessing the rest of your house or apartment.  Try to make use of outdoor space when possible, because that will always be a help.  If it is not snowing like hell, or 20 below outside, there are plenty of activities that can take place outside.  My brother and I used to go out and just cross country ski(something we did not really know how to do) and build a fire in a sheltered spot to have a barbecue in the forest.  As it happened, we were on what was our parents' old farm, where we sheltered inside a hedged garden that had become overgrown over the years.  Winter or summer, make use of outdoor spaces.  Why relegate use of a patio to the summer months.  This may be crucial to your ability to live in a small space.  My sister and her husband spend long hours in the morning, walking in the woods and along old logging roads both summer and winter.  Those days when it is too cold to feel your nose after ten minutes will make you grateful for the warmth and cozy space that you have created inside.
Will you be off grid when you build your house?  If so, pile a few books on a side table, bring in a few games and perhaps a puzzle or two.  Write letters, begin that novel or genealogy project you have been planning.  Live in that small space for a long time before you make a final decision.
The fact is, that if you can stand that, you will probably do even better in your new house.  Your kitchen and dining room were not meant for total living, but your well designed compact space will work much better.
In browsing the Internet, you will see whole houses on the back of a pick-up truck or on the bed of a horse trailer. In those spaces, clever people are able to carve out private study spaces, bedroom lofts, kitchens and bathrooms.  Surely if you are not restricted to 8 by 12 feet you can make a perfectly functional home.
I have a real problem with my perception.  I absolutely cannot concentrate on anything if there is significant noise around me. Someone plays a radio in another room and I have to close up my book and toss it aside after reading the same paragraph four or five times without comprehension.
The real question is: Can you spend the rest of your life in the same small space with another person, or even with a family?
The solution is to build bigger.  An extra 10 by 10 space may make all the difference in the world.  The Italians have tiny wood stoves in their houses.  Soooo cute.  There are also wonderful tiny propane heaters available that would heat up a space like that in minutes.  There is something alluring about the idea of a tiny pavilion in a picturesque spot or at the end of a garden path lined with shrubs, and it would cost almost nothing to build, using Craigslist salvaged windows and shingles etc.  A tiny wood stove with a finely split hardwood woodpile outside the door(Stove wood they used to call it when Mom had the wood cook stove.) could turn an intolerable living situation into a real retreat.  You just have to live with the fact that you will have no water or other facilities there.  There is always a Lavabo set-up or pitcher and bowl from the 19th century(see notes on ceramics later) for a quick wash of the hands after peeing in the snow, but you could easily spend a creative day in your private retreat, or run your accounting business or write lesson plans from your desk in your pavilion. 

Just a quick caveat.  Do not store cord wood or stove wood against a wooden building.  Beetles and vermin love woodpiles, and that would be an open invitation to start spending time in your retreat.
I would perhaps keep the woodpiles at least ten feet away, though you might get by with less.

Your new home will have to be neat.  Can you get rid of most of your STUFF?  What will you take with you to your new home?  Certainly there will be family antiques or keepsakes that you can pass on to children or siblings.  But, do not think that you will have to get rid of everything and start over.  I have wonderful 17th and 18th century French brass candlesticks and wall sconces that belonged to Roman aristocracy.  I will certainly use those, but I may pass the dozen or so 19th century ones on to someone else. 
I will have to decide if my new house will have some sort of temperature and humidity control in it.  If I am going to be rustic, I will probably  pass my 15th century manuscript pages on to someone else.  They will not fare well in dampness, heat or cold.  My Staffordshire plates will build up expansion and contraction stresses if my house will be hot or cold for long periods.  I was once in a friend's antique shop soon after they reopened in the spring.  It was a very warm June day.  We heard a PING and a bit if rhythmic scraping from a high corner of the shop.  A huge Leeds platter had been standing against the wall on a high cabinet for several years.  The ping was the platter splitting entirely in two across the narrow axis of the oval and the scraping was the two halves rocking back and forth against the wall.  When we tried to put it back together, the two halves did not fit anymore.  They became tiles in a garden wall.
I was working in a fine jewelry store some decades ago, when a woman entered the shop in tears.  She was carrying a twisted and crumpled piece of gray metal.  She had left an 18th century pewter Revere style bowl in her attic.  It had belonged to some great great great grandparent, and the heat had softened and sagged the bowl into the packing material in the box.
Likewise, textiles can become mildewed  and moldy in the presence of dampness
Wood can split in heat and dry, and swell and crack in dampness.(There are little chemical filled plastic tubs available that pull the moisture out of an enclosed space)  I have seen many tables that have been moved from England to Arizona and on to New England.  They cracked in the dry southwest, leaving a half inch gap between the halves and then they swelled shut again in the move to New England.  Problem solved?  Not really.  There were ugly splits in the finish, and they never quite resume their original shape.
Be critical in your editing.  Choose things that will stand up to the new environment for your new home.  If you will have access to electricity and the house will not be empty for long periods, then you can probably take anything with you.  But remember that many things should do double duty.  A dining table will also be your desk.  Candlesticks may be stored away for long periods, but will be essential when the electricity fails.

Ok...you have been in your tiny space for a couple of weeks now.  Do you still think you can do this?
Now you know if that will be enough space for you.  If not, then you know you will have to think a little bigger, or think about private and separate space for your poetry writing.