One.... stop using functional strength as a term. There is no such thing and it makes everyone think you're a giant douche-nozzle. There is only strength. You can get deeper and talk about limit strength, speed strength, et cetera, but functional strength is a false term. Any strength is functional if it is useful for whatever force you're trying to apply.
Bodybuilding aesthetics are very hard to achieve. Nobody is going to casually look like a bodybuilder. It takes serious work to achieve what they do. If you want to be lean and muscular, then you're in the same category as most of us. While there are some fatty powerlifters on this forum, most of us do S&C for some sport. If you want to get stronger, then you have to train strength. The best way to train strength is through barbell workouts on the big movements such as back squat, bench press, deadlift, powerclean, standing press, barbell row. You should look at a basic strength training program to find out when to do what movements and for how many reps. Starting Strength, Madcow, Stronglifts are all good starting programs. These programs focus on increasing your strength rather than increasing your mass. Generally the more reps you do, the more you tear your muscle fibers and the more you grow. If you want to stay lean, you'll want to limit your reps to 1-6 and have long rest periods. If you want to grow, you'll increase the volume to like 6-12 reps and have shorter rest periods. Bodybuilding workouts have a lot of volume and isolation exercises compared to strength training programs and you'll not become a bodybuilder by accident. Strength training programs focus on 3-4 major compound movements each day with the intent on adding weight each time. It's focus is efficient muscle use and training your CNS. Bodybuilding programs focus on hitting each muscle group from multiple angles to cause tears in the fibers and create growth.
As far as how large you actually get, that depends on your diet. You can limit your growth by controlling your caloric intake. The Diet sub is the best place to figure those numbers out. You can do all the strength training you want, but if you don't eat to grow, then you won't grow. You'll get stronger and lean if you stay on a limited caloric intake. You'll get stronger and bigger if you stay on a caloric surplus. The right amount depends on your size, activity level, training history, metabolism. You'll have to tweak that.
My personal advice is this. Get yourself on a beginner strength program. Do some good cardio when you can like swimming/sprints. Clean up your diet and cut out sugar and fried foods. Give yourself a good 6 months of just focusing on that and see where you wind up. I'll bet you cut a bunch of fat, get strong as shit and you won't look like Ronnie Coleman. From there you can figure out what you truly want.
