Hey there, thanks for the question… I have tried to help others in this exact same scenario in the past. The best success came from doing once change at a time, unless the all the changes are absolutely necessary for health reasons. Changing your diet AND adding an exercise routine is very difficult… but add quiting smoking to that is a recipe for failure. Try just going to the gym and quitting smoking, but focus on the “not smoking” part for a couple months. This will give you some time to kick the withdraws and then you can focus on your diet and gym routine.
Hope this helps.