New to this, please help

Please have patience, this is a long post

My son is 6 months and a half. We started solids and he would eat 2-3 snoonfull of some vegetables i prepped for him. Last Thursday i made a mix puree from all the veggies he already tried: zucchini, avocado, red pepper, potato, chicken meat and some wiped bone marrow. He likes it and ate maybe 10 spoons, so definitely more then the other days. 2 hours and a half later, he vomited and continued to vomit (5 times) till all he vomited was yellow. He was very pale, lethargic and we went to urgent care. The blood tests showed a bit elevated white blood cells and also C reactive protein. They could not determine why he had that reaction and considered a stomach bug. They hydrated him intravenously. We then went home and the next days he was fine. Three days later i offered porridge with a bit of avocado. (This is the comon food in both cases) He ate about 5 spoons of it. 2 hours later, same reaction. Vomiting (5-6 times) very pale, low temp to the forehead (36.1 with a non contact thermometer when normally he has ~36.7).

He got a bit better after 2 hrs so we didn’t go to urgent care. I gave him some milk (pumped breast milk) and he is now down for sleep.

I already read this: https://fpiesfoundation.org/about-fpies-3/. And can see how the reactions listed there happened to us.

I have some questions:

1. How rare is this: i spike with several pediatricians so far and none mentioned this. They all sayd i gave him too much,
2. Could it not be just the fact that avocado is hard to digest for his age and not be FPIES?
3. Do we need to go to hospital every time a reaction happen?
4. How often is a sepsis like shock happening and what exactly does it mean? Is this a life threatening condition?
5. How many foods can trigger a reaction? Could it be just one or two?

I am horrified about introducing next foods and have no ideea how to go on from here. Please, please share your journey.

This is my second baby. My first is 6 years old and he had allergies to: casein and egg and now to dust mites (also has viral and allergy induced asthma) so i had my share of scares and hospital shares. But this FPIES in completely new to me and others apparently