You are able to craft anything if it exists, if you know the recipe, if you have the skill and if you have the materials.

There are many crown items available - some craftable and some not - there is no list this one she knows of that shows the crown only items though.

You cannot really farm many furnishings - although you can get letters from pickpocketing scholars and cloth sometimes from stealing from crafting areas.

Master writs are quite random but having researched as many traits as possible and knowing as many motifs as possible apparently increases the chances.

Which server and platform are you on traveller?

Yours with paws
Santie Claws

Also don't forget about the luxury furnishing vendor whose goods change every weekend and also the regular and achievement furnishing vendors in the main town of each zone.

Yours with paws
Santie Claws

There are also Home Goods Furnishers and Achievement furnishers in each major city in each location that sell furniture (and there are lots of good stuff that you can't craft and sometimes event can't buy in crownstore).

You don't need to buy anything with crowns except very high priced manors or moderately high priced furnishing bundles (but only if you think you really need it). I manage to furnish my houses decently with 97-98% of non Crown Store stuff.

You farm furnishings mostly by stealing or fishing

Concerning Master Writs, I would suggest buying them from traders (the ones that you are able to complete) and join a guild that has all crafting stations (for rare sets too) in their guild house. Also I suggest using "Dolugbon's lazy writ crafter" addon (I hope I wrote it correctly) which will help you a lot