I'm two recipes into my new Instant Pot (yogurt and hard boiled eggs, started with the basics :D) and I'm planning my third today. I haven't added any accessories yet beyond replacing my cloth pot holders with silicone in order to be able to remove the inner pot more easily and safely. However, I have a few things on my Black Friday/Christmas list, based on what I've done so far and what I plan:

• spare sealing rings - I'm looking at the red/blue set so I can have one for yogurt, and one to rotate with the stock ring if I do something stinky or just want to wash it between dishes
• second inner pot - I think I'm just going to get another stainless, but looking at today's meal prep plan I'd really like to be able to just yank the pot of chicken out, and drop in a pot of cubed potatoes without having to empty and wash in between (not doing them at the same time for Reasons.)
• Silicone Steamer set this is low on my list, but it's the one I'm looking at for doing any pot-in-pot, and possibly for being able to stack eggs more easily than with the standard rack. For your meat + vegetables I think this would be more important
• glass or silicone lid - I haven't decided which yet, but especially when I get a second pot I'd like to have a lid I can just put on and toss the whole thing in the fridge, either pre-prepped or post-cooking. I'm leaning towards glass because I could use it for sauteing (I think) and for slow cooking if the Instant Pot replaces my slow cooker (experiment forthcoming over the holiday break.)

Even buying all of the above as "genuine Instant Pot accessories" from Amazon the total cost comes out to under $100, which is not a bad deal considering the utility of them.

This is something I'm going to try with other recipes, but I don't want my mashed potatoes flavored of lemon butter chicken, so things like that will be kept separate and done in pot-after-pot. :D

As for a separator, I haven't tried it yet but I think the steamer rack in this Instant Pot Steamer Set will stand up higher. If not, take a look at the "egg" stacking racks referenced in the "Customers also bought" list on the steamer set page as those should definitely stand taller than the stock rack.