Got a quick question about this. Ok so I know there's a little text you can click on that says "Buy more?" and brings you to a page that says it costs 1500 CSC for my 11th slot. I also noticed the other day there's an item in the Millionaire Center listed as "MC Pet Slot " but called a "Loyalty Pet Slot Totem" when hovered over for 20 million sP that's described as unlocking a pet slot. So are they really just the same deal just with different currencies or is there a nuance I'm missing between both?

they are the same deal, in that you get a new pet slot...but there are a few differences.

The Cash Shop one stays at the same price right up to the limit you can buy (max 55).

The millionaire center ones get more and more expensive as you buy them up, and they have a lower max of 25. They go up in price by 20M sP every time and I think at some point they cycle back down to 20 Million starting price and cycle up again, but I'm not totally sure how that works.

There's a breakdown on your user dashboard that looks like this:

The Millionaire Center slots go up in price by 20m sP up to 200m for the 10th slot and then start back over at 20m for your 11th (and then increase by 20m with each slot again). I'm not positive if the pricing starts back over at number 21 also? But I'm at slot 14 which costs 80m so I can confirm the first part is correct :)