Looks like I might have fixed the issue! @ravasheencc suggested I re-do the deco slots on the top to match regular island counters, and I was able to load this thing up with a whole bunch of jars of chilis with no issues!
Using the moveobjects cheat seems to be fine now, so you should be able to decorate to your heart's content! There are plenty of slots on the shelves, just make sure there's clear space for your sim to cook or it'll look a little funny :)
Also, spare a thought for my poor freegan testing sim. He was upset at having to waste so many ingredients for salads, haha