Fascia tends to be the limiting factor in arm development. The guys you see in the mags with huge arms have done Pump and Pose, extensively, and allowed the muscle to grow into it. It's permanent, and it's just MCT oil. Think of a hot dog casing that you inject liquid into, then, drain the liquid and put more hotdog filling into....just like that.
Sarcoplasmic hypertrophy involves getting the fascia full of fluid, either by high reps, or by MCT oil, etc. It DOES NOT involve high weights.
Bodybuilding, at least in competitive and pro levels, is very much a cosmetic pursuit. Think "Hooters" for guys. This involves a long list of tricks, but, methods that are well known within the community.
Unless you do high reps, and eat real good, or blast a couple of programs of MCT oil, you won't have 20 inch guns, prometheuscowboy. It doesn't work like that. You have to expand the muscle fascia, and very few folks can do that just getting pumped up. Those guys you see with huge peaks, and 21 inch arms are almost always resultant of pump and pose and pumping. Kinda' like a chick having a boob job. No magic potion will give you those huge arms. The fascia has to be stretched, one way, or another.
The upside: it's permanent. Once you grow into it. It's their forever. The downside: it hurts. You're forcefully expanding the wrapper around your muscle.
Ask your buddies at the gym about it...they'll tell you if they trust you.
I've met national level competitors that were "pump and posed" head to toe at the age of 15. They end up with exceptional "lines" but like many things involving beauty in culture (e.g tattoos, boob jobs, nose jobs) it's not without pain and some level of risk. Their look is by design.
Some guys get carried away, and have 20 inch thighs (tiny) and 24 inch arms, at, say, 5'8". That doesn't look freaky. It doesn't look huge. It looks stupid. Greg Valentino is a good example of someone who is an idiot with it.
Rest assured, though, it's part and parcel of competitive bodybuilding.
If you were to have 20 inch arms at 5'8" and only 180#, it'd look over-done. It really probably isn't something for you to strive for. You'll get more points with balance.
With regard to your chest: high reps, high volume, plenty of calories, adequate recovery. Repeat. Incline presses and incline flies, with dumbbells, through a full range of motion, will be your most effective for sarcoplasmic hypertrophy.