have to have the store to have access to the market in the first place. more of that room will not change the store's inventory.
if you have 5 farm plots, you have 5 buildings producing flowers.
i do not know that the shop's inventory can be manipulated like this. it's generally pure RNG. if anything affects it, it's restocking more of the same thing if you buy them out... but that might just be observational bias.
i'm also not sure a table is actually a prop that can spawn in the shop. i know keepherdev has the assets, as they are used in dungeon raid her, but i cannot actually ever remember seeing one in the shop, myself.