I don't think we could ever be fully prepared. He turned 7 months at Christmas, and went on diet a few weeks before. We also had 6 months.
Look at it this way, we (cause you sound much like me) found out all we could. I never came across information on specific diet needs and breakdowns, as they vary with each case/child. Trust me when I say, it won't take long, and it will all be second nature.
We had previously explained to family Jake's inability to break down proteins, and how we were sure he would be allowed meats, eggs, and peanut butter..those types of food. Even then, everything was still questionable about his allowances, however, we would learn as we go. We thought we were prepared and informed.
December the changes happened for us. The day they said he is going on diet, we felt like we were back at square one. Everything seemed so unclear. So many questions. I am not a dietian, how would I ever know how to feed my son?
Couple weeks later, we saw extended family for the holidays, and knowing he was on diet, we were asked many more questions. We answered them all like pros!! We had information we couldn't have imagined knowing just a month before. I now know that 7 grams of rice cereal contains .5 protein, and will count as 1 point for him. I know that the the reason some cereal says add water instead of add formula or breastmilk, is because the add water, has a milk base in it. I knew that if I watched the labels, I could decide what was low in protein, and can begin guessing on what will be better choices for him. I also learned that on food labels, if its less than .4 grams of protein, they can round down to 0, however if the food contains more than .5 they need to round to the next whole number. Who knew that stuff??
I will admit, I am not self-reliant yet, and am not embarrassed to admit, this is a long learning game, and I still have far to go! I was confident enough to allow him a Rice Rusk over the holidays while his dietian was away, and he was wanting to feed himself, and we were wanting him to try, so we can enjoy our meals. However, I was uncertain enough to fire off an email asking for the reassurance that it was a good choice!
You will be fine. We are very lucky in Canada, we have a ton of resources, not including each other.