It is a steep learning curve.
Yes you are right to start from basic foods.
Some foods might be "tolerated" however this does not mean "safe" It means some HFI people can just about eat them, however any quantity will cause problems.
With FM people it is the ratio as you say and also sucrose is not an issue for them.. it is for us.
Leaf herbs are safe in any quantity they are likely to be used in food. This adds a great addition to the flavour of what is basically a meat, dairy and starch diet.
Cheese are also used by almost all of us as a key food source.
Cheese is high in all the good things growing children like and need.
At one time many HFI'ers were dying from eating large quantities of glucose which it turns out was contaminated with Fructose.
Glucose is supposed to be "safe" however all of it is made from vegetable origin.
No attempt is made to remove any fructose in any plant material used to make the glucose (usually Sweet-Corn also known as Maize) in the manufacturing process.
They thought it was safe because they did not get any immediate reaction..
However after an hour or so they would feel very unwell and hypoglycaemic so would have some more.
Because of eating so much Glucose their teeth all rotted away quite quickly too.
One good benefit from being HFI is we never get any tooth decay at all unless we eat glucose.
Keep smiling all will be fine.