Yes you can make the house bigger but you need to be careful, you can only build one wing at a time and it is a permanent thing as you build it so make sure it is what you want.

The small house is the starting point for all the homesteads adding the main hall is the next step, once you build it the small house can then be remodeled into an entrance hall for the now larger house. Check the homestead page here for the step by step guide.

Make sure you do not leave things in your chest in the small house when you remodle though, because the chest will no longer be there once you remodel.

So, what I understood so far - I take all my stuff from the small house, build the main hall, and when I remodel the entryway all furniture will be gone?

Ok I built the main hall and furnished it almost completely... except the fireplace as it's missing from the workbench. Any ideas for fix? (I'm on PC)

Only entering and exiting the benches menu a few times or leaving the house fast traveling away then trying again, you can turn those smaller ones on and off from the main bench outside too (but careful as that option can disappear sometimes as well).

A Steward might be able to do it for you if it still doesn't appear they add every item to a room though if theres anythings you didn't want added (and they usually do it slowly).

Thank you, I paid the steward, looted a couple of dungeons and when I came back it was fixed.