Eisvogel,
Don't worry too about the doctors and authorities. Most will be only too pleased to try and get you in the saddle.
Yes, there are rules and hurdles to be taken on the way to passing your medical etc.
More important is the decision whether you want to invest in a career that can be ended by the stroke of a pen if you develop a disqualifying condition.
If you have a chronic condition that maybe of even more significance.
Consider that it would be devastating if you invest all that money and lose your medical soon after passing your ATPLs. Loss of licence insurance may well be difficult and expensive to obtain and probably exclude any pre-existing conditions.
First step would be to find out what the likely outcome of your chronic condition is in the long run. Then go and get a first class medical and consider your options.
Best of luck
FD