Hi, I’m hoping someone who’s experienced in object footprints can
help me with this one:

I have some experience in SimPE (but still not an expert) and do know how to clone and create 1x1 and 2x2 tables, but I am trying to figure out the best way (or any way) to make a large round 3x3 table with enough room to seat 12 sims, the images posted below are examples of what I’m going for.

Since there's no 3x3 tables to clone from, would it be as simple as going to OBJD and expanding tiles like a regular object, or would I have to do even more to the mesh to make sure that both the sims and chairs interact with it properly?

I've never done this, so it's just a guess informed by making other objects. If the table you clone doesn't fit 12 Sims, just adjusting the footprint isn't going to be enough. You'd have to study how tables work (how chairs connect to them and how the food slots are made) and add your own additional slots. Or maybe you could slice that table into 4ths and move the plate and chair slots until they're around the outer ring, then place four of them together

Here's a good tutorial about expanding footprints, I followed it to make a functional 4x4 tent recently: https://simfileshare.net/download/1450599/
as well as this tip to use only one OBJD for multi-tile objects: https://crispsandkerosene.tumblr.co...post-obj-l-anon

regarding slots, this tutorial by HugeLunatic is a good starting point, and it has links to other resources for more advanced slot editing: https://hugelunatic.com/151/

The trickiest part in my opinion will be to make chairs behave as expected. As far as I understand there's a bunch of BHAVs in the chair semi-globals controlling the detection of nearby tables and deciding whether the chair should be pushed in/out of it. So if you're lucky expanding the footprint of your table might be enough for it to be recognized, and chairs might do the rest of the heavy lifting themselves... but I have never tried and things are rarely that simple with advanced object editing

very ambitious project in any case, when something like that comes up I always think, there's probably a good reason why it has not been done so far, so good luck!