I was of the understanding that both mortgage *interest* and property taxes are deductible as a percentage, as is insurance, electric, gas, maintenance, etc.
What you don't want to do is depreciate the percentage of the house used for work, ie claim capital cost allocation. THAT triggers cap gains/recapture.
That is on a T2125 not employee. If I bought a larger house in order to have a room to work in, that leads to higher property taxes. No reason I can see that that would not be deductible.
You can either do square foot percentage, or number of rooms, as long as the calc is reasonable. And yes, if you convert the room into a sewing den over the weekends you must prorate.
Capital improvements - no. So upgrading the kitchen to granite (increases resale value), no. Replacing broken kitchen stuff with similar, yes. Not that you likely would for a kitchen, but I claimed (a percentage of) a driveway and new furnace a couple of years back, I believe. I read through everything - I had a driveway, it needed replacing, we replaced it. Ditto the furnace. Neither is likely to significantly increase the resale price.