Hi Chris… I too am (still) a memory student, so take my input as just another ‘artists opinion’. Your first question regards your memory palace and whether rooms should/could be used as confined elements for specific use cases…. So I would start by saying be sure you’re using the right tool for the right job. I think of a memory palace as a tool for memorizing an ordered list (a procedure, directions, U.S. presidents in order, etc.). So your palace is an environment that you travers in a specific order so that you don’t confuse yourself upon recall.
In your example of using the kitchen to remember the grocery list, what you are suggesting is that … even though the kitchen is not the starting/entry place of my palace, there is a significant demark (kitchen door) at the start of the kitchen area of my palace, and it is natural for you to know that, for grocery lists, you always use your kitchen, so you know to start at the kitchen door for recalling a grocery list.
While that can work for you, if grocery lists are something you do routinely, you might keep your palace clean and develop a tour of the inside of your refrigerator or something like that, specifically for your grocery list. The only reason I suggest that is that when you attached multiple items to your loci for different lists/purposes, it becomes a recall challenge unless you’ve rehearsed a few more times than would otherwise be necessary.
I’m not sure I’m interpreting the intent of your second question but my sense is it would be better answered by someone who routinely uses a memory palace for multiple lists simultaneously. While I have done it a few times, there are others on this forum that would be able to provide both of us some pointers.
For your last question, using a memory palace to remember numbers, you certainly could but efficacy would be a question of your situation…. Are you memorizing multiple numeric strings, then how to treat the breakpoints, etc. There are a few blogs and books written by some of the folks who have won competition where they talk about the systems they use…. Worth a bit of research if you are not happy with the performance you are getting out of how ever you are doing things now.