D&M,
I have tinnitus in my left ear - high freq loss at 6000 and 8000Hz. They are only really interested in the lower speech frequncies, so I wouldn't worry. The standards are fairly liberal, and are less stringent for renewal. Anyway, as long as you can hear a quiet conversational voice at 6 feet, in each ear, with your back to the examiner, you should be OK.
BMI? They do weigh you etc, but I don't think you would fail the medical for being overweight. You would only fail if this caused a problem in terms of BP or cholesterol, or if you had a history of cardiac events in you family.
Asthma? Talk to them about it. They may ask you to do the lung function test, and then get you to do it again after you have run around the quarangle.....yes, I'm being serious!
Just be honest.....they are there to help, as I found out when I went for my Class 1 in June of this year. I was fractionally outside the old eyesight req., but because my prescription was stable, and I was 26 years old, they were quite happy to issue me with it.
Good luck, and drink plenty of water before the medical, as you have to give a small sample. Oh, and take toiletries.....you can have a shower after. The gel they put in your hair for the EEG is erm, well....very yucky!!
Regards
Barney