So I want to provide rich details and options for my PCs, but there are a couple things I’m having trouble with.
For example, when it comes to fruit, grain, etc., are the fruits still large (compared to the mice)? If so, how do they harvest them? Do mice have a special type of grain crop that is their size?
Do the mice get milk, to make cheese and things? Or is that just left out?
Any other relevant information you guys can provide? Thanks!
When I describe the orchards of Appleoft every apple is the size of a wagon and the mice have to use block and tackle to harvest and transport them. It’s a massive undertaking.
They mostly harvest the crops wild. Notice there is a Harvester skill, but not a Farmer one.
The crops are normal sized, not mouse-sized. The only livestock are insects, so milk is unlikely.
You sir, obviously have never seen the comando milking teams of Barksdale!
Mouse Guard fishing: Very similar to whaling. Extremely dangerous but one catch can feed village for a winter (after it’s salted and smoked of course).
In the campaign I ran, one of the big deals was the autocratic leader of a mouse town trying to force the adoption of farming methods in place of the traditional harvesting of wild seeds & nuts etc. Such forward planning and focused labor was not entirely compatible with Mouse Nature as I envisioned it, despite the promise of a more dependable food source.
Thanks guys, lots of good stuff here.
In my recent game my players needed to take some food with them and I (as a NPC) told them to take dried fruits. I depicted a big storeroom with a wide enterance. There was some mice dragging cart that has one normal sized apple in them. At another corner I said, there was some other mice cutting fruits that have delivered and then leaving them under sun on blankets.
It was a nice part, helped them to visualize the daily life in Lockhaven.
When it comes to milk, I myself can’t drink/use cow milk in cooking, so for me it was easy to think that mice DO have milk. Nut-milk like me. 
And for cheese, I went with Redwall and introduced cheese made of nuts too. The animals in Redwall loves food, so there’s lots to learn from descriptions of food in the Redwall-series if you want to do a food-centric storyarch.