Thank you so much for all the tips! Ik studeer in Vlaanderen 
I actually prefer leaner cuts because buying fat is cheap per kg. I just bought some lean steaks for 30% off at Lidl and ended up paying about 4-5 euros/kg. One is gepelde steak and the other is minuutesteak. They're both incredibly lean.
I haven't been vegetarian (just plant-based) for a year. I did eat some chicken and turkey on occasion. I know that my body doesn't absorb nutrients too well from plants + insulin resistance is just not a good combination and I think my health will benefit from this.
The taste of red meat... ugh. Honestly, I have to eat it with eggs to tolerate it. I love raw egg yolks on my steak, though. Some cheese does it favors too, haha.
Do most butchers around here have organ meats? What would you recommend for beginners? I haven't seen beef heart yet, but I do want to try it.
I do plan on reintroducing fermented veggies after zero-carb for a few months. I made some sauerkraut a few days ago and will refrigerate it when it gets aged enough for my taste.
Regarding organ meat availability;
supermarkets sometimes only have chicken liver. Some others carry pork liver as well.
Butchers will usually have at least chicken liver and pork liver. Sometimes you can specially request beef liver, lamb liver (lamb liver is pretty mild compared to the others) because the butcher doesn't have it in their display case up front.
You rarely see kidneys in the netherlands. I had to ask for them at the butcher and they had them in the freezer.
Liver and kidneys are usually cheap even if you get organic. And it's worth getting them organic because they will taste a lot better. IMO conventionally raised pork liver tastes like garbage.
If you can eat full fat dairy (cheese, creme fraiche, sour cream, cream, cream cheese) that will make the diet a lot more convenient and tasty.
I live just over the belgian border in the dutch city of Breda. Afaik vlaanderen has some great charcuterie. I think that's good as a treat.
Sounds like you got a great deal on those steaks. I buy steak at 18euro a kg at the Albert Heijn supermarket.
I also have IR (it used to be more severe in the past though) and IBS and I found that eating mostly meat/fish/eggs/butter and figuring out my macros was the key for my well being.
I've reintroduced some plant foods and only kept those in my rotation that didn't interfere with my progress regarding IBS and weight control.
Doing pure carnivore in the past was a great way to give my bowels some rest.
Regarding the taste of red meat; you don't like steak pan fried in butter? Beef heart tastes pretty much like steak to me. Perhaps a little milder.
Everyone has their preferences of course. I prefer lamb. I don't really like pork. I will randomly just lose the taste for something and not want to continue having it in my rotation.
I ate salmon for a while (oven baked) and just got tired of it. Steak and scrambled eggs are two things I haven't gotten tired of and I've been eating those for a long time.
I wish I could eat cheese and cream on a daily basis but sadly that interferes with my weight (even if I keep it within my CICO budget). The zerocarb subreddit has a lot to say about why that happens. It has something to do with IGF-1 (insulin-like growth factor) and how it effects some people with IR.
I recommend trying out canned cod liver, canned sardines, beef liver, lamb liver, lamb kidneys, salmon from the frozen section, shrimp, ground lamb, frozen squid, and visiting not only supermarkets and regular butchers but also butchers that cater to the turkish/moroccon demographic. They tend to have lamb cuts they other butchers don't.
I think from a nutrition perspective I would recommend against buying chicken livers and pork livers.
What kind of cooking methods do you have access to? Slow cooker? Oven?