Yes, think ahead, but I'd probably suggest to not try and think too limited - if you can cope with things in the first few years, then once you have got through all the basic and specialist study years and have the status of a consultant you may well be able to move into other areas (like more research, or private practice, or setting your own hours) if things get bad - which there is no guarantee of anyway. I think you are right about knocking out possibilities like surgery right away, but that still leaves quite a lot. Rather selfishly I'd say strongly consider rheumatology - would be great to have a few more rheumatologists out there who really understand what they are trying to treat.