-when you fill the form for H&C application, there is a question asking what kind of exemption you are requesting for. Clearly provide details over there and request exemption there.
-I am not sure how long it can take as I am myself waiting to get medical exemption.
-I don't know if there is specific list of inadmissible medical condition. There are several factors they consider for medical inadmissibility. 1) if medical condition is risk to public health and/or safety, then that makes you inadmissible. 2) if your medical condition treatment cost exceeds $108,990 over 5 years (or $21,798 per year) then that's also considered as inadmissibility.
Just today, i came across this document of ontario which includes how much ohip pays for each medical service to hospital/any other healthcare provider. If you don’t know how much your health condition will cost yearly, refer this document and calculate the cost.
https://www.health.gov.on.ca/en/pro/programs/ohip/sob/physserv/sob_master.pdf
If you ask hospital directly about the service charges, they will give you a quotation of 5-10 times higher than-amounts mentioned here. The reason is I found after reading a lot is that hospitals are allowed to charge higher to uninsured patients to generate revenue and discourage providing services to uninsured.