Partitions and Iron Fences are valuable items that aren't found often.
It's a good idea to balance out each facilities' expansion at LV 2.
From then on, facility expansions can vary based on playstyle.
Expanding the Workshop will provide an advantage in battle by crafting better equipment; expanding the Bedrooms will increase bonds more quickly; and expanding the Warehouse will help with item management.
The LV 1 Toilet helps relieve the Bladder gauge, but will increase Stress when used. Toilets found in drifting ruins, such as the one found in Mashiro Garden Tower 1F, can relieve one's Bladder without increasing Stress, so be sure to make good use of them. However, don't hesitate to use the Toilet in the base when necessary, even if it does increase Stress a bit.
There isn't much need to expand the Toilet on Difficulty I since the Bladder and Stress guages do not increase, but you should still consider it out of courtesy for the characters.
Harvesting, hunting, and fishing are easy ways to obtain a variety of materials. Some items can only be obtained at Harvesting, Hunting, or Fishing Spots, so be on the lookout while exploring.
Items at these spots will be available again when the day changes after exiting ruins. Be sure to manage character inventories well to avoid carrying too many items.