Secret to a good broth is not only your aromatic veggies and bouquet garnis and peppercorns (I use a garni of parsley, bay leaf, thyme, and sometimes basil and oregano depending, and sometimes a little tarragon and marjoram depending) and salt along with carrots, onion, garlic, celery and sometimes ginger coins and star anise (depending on the type of broth). I like brown stock even for chicken broth so I do a few different things...one is that I will brown the meat in a pan of oil/butter till very dark, then put it in the stock pot. The other thing that I do is buy extra parts: chicken necks, wings, backs anything with the most bone. Thighs and legs are ok but I am looking for cartilaginous bones and skin mostly cuz that's where the flavor is. I can sometimes get carcasses from my butcher too! He gives them to me! In that case I throw all the aromatics and bones into my huge roasting pan and roast the tar outta them on 450 degrees until it's all browned and good! I stir to rotate the bones. Then once the bones are all good and browned I put the entire contents of the roasting pan into the stock pot and let it simmer (never boil) on low for about 3-4 hours. I will strain it after that time and continue cooking the stock to reduce it to the right strength. It usually takes me about 8-12 hours to make a good rich stock.
I use the meat off the bones (even the neck, wings and back) to make things like my family recipe of chicken salad or make things like chicken pasta salad or I add it back in at the end per portion (meaning I add it to each individual soup bowl) for chicken soup with "whatever" (rice, veggies, etc). I also sometimes use it for chicken and dumplings or king ranch casserole or those things.
I never end up needing to use msg, kitchen bouquet, or bouillon or base. The secret is having as many bones as possible and as big of a stock pot as possible and long and slow simmer with colored bones, good veggies and herbs.
In my experience, the meat gives very little flavor to a stock. It's the taste that comes out of the bones and the skin that make a stock worth it's weight in gold!!!
Cool it completely then put it in the fridge. The real sign of a good stock is that it's gelatinous when chilled down. You will be left with a hard layer of fat on the top. If you want to reduce the fat in your stock you can skim off some of it after it's chilled down but for God's sake keep it! It's called schmatz and is awesome to use for cooking things like browning potatoes or potatoes fondant or browning veggies or starting sauces. It's also great as the fat in dumplings and matzohballs!!!
As for how much water? I want my meat/bones and veggies to always be covered with water while they are simmering in the broth. I have been known to even put a layer of parchment over the top of the broth while it's cooking or to put a pan inside the stock pot that is weighted a bit to keep everything submerged. Once the main cooking of the bones and veggies is accomplished, you can let the stock reduce. Also, you can remove the chicken with the meat portions (legs thighs breast etc) after about an hour. Let it cool enough to tear off the meat and reserve it - covered, to cool. But add the bones back into the stock with the rest of the browned bones...in order for it to cook.
Because I brown my veggies in the roasting pan, I don't bother about making the traditional mirapoix. I actually want the caramellized bits of the veggies and if there is stuck on goodies in the bottom of the roaster pan after roasting...I will deglaze with some vermouth. I will also sometimes add a splash of vermouth or sherry to my stock too. It just depends how heavy a taste I'm wanting...or if I want it purely for stocks and bases for other sauces.