1. To start building muscle it depends on what your build already is, if you are not very strong I would HIGHLY suggest starting with the basics, start using your very own body i.e. Push ups for your upper body, plank for your core, and squats for your legs, also try to do some curls to work out your forearms... basically if your not in shape than do this. Depending on your physique you may want to add somewhere around 30-50lbs of resistance while you do those exercises to be more efficient. Doing around x200 of each a day could work out pretty well.
Other options would be sandbag training, depending what you are doing its a good workout and conditioning... depending on what ones you choose(and if heavier amount) do 5 sets, of 5 exercises and 5-6 reps of each with 30 second breaks in between each set, shouldn't take more than 15-20 minutes. With a sandbag you can also do deadlifts, snatch's etc(if you don't know a particular one look it up)
Just general conditioning and work outs are a must to be able to stay in shape.
REMEMBER TO TAKE 1-2 DAYS OF REST! IF YOU DON'T YOU ARE WEAKENING YOUR MUSCLES!
The other half of this is the DIET, a DIET is a MUST! Here are some groups that you should follow, I wont list out exact foods but it isn't that hard to figure out if you ever did a sport that require strength. Also this changes if you plan to gain weight(bulk) or cut weight(loose)
Things to Take in(eat)
*Foods high in protein i.e. Eggs, LEAN meats(chicken)
*Red lean meats - pork etc
*Veggies(NOT with crap on them ie fatty sauce) these are good steamed espically carrots and green beans
*Whole grains and wheat, oatmeal, cream of wheat etc
*Carbs (if your cutting avoid these)
*Sometimes high calorie foods
*General healthy stuff
*Creatine(not too much as you get watery) helps add a few pounds here or there. Dont worry its naturally produced in your body, you just dont use it
*Vitamins - one a days' coture stuff etc, you don't get all the zincs as stuff you usually need to become strong a day so having 1-2 of these sorta things would be a good deal
Things to avoid
*ANY sort of fats
*If its unhealthy=Avoid it, plain and simple
Example of a days diet(mine from awhile back)
x2 cooked eggs(not greasy, grade A)
x1 Slice of whole grain toast with a side of natural jam(DO NOT get the fatty sugary crap)
x1 Fresh banana
x1 Small cup of skim cottage cheese
A spoon of peanut butter
2x Peanut Butter Protein diet bars
x1 Protein shake
x1 Whole grain bread with a slice of lean pork and lettuce
x1 Slice of lean chicken with lemon sauce and spices
Brown rice with a little veggie dressing(-20 calories, 0 fat/badness)
Veggie salad with peas' lettuce, carrots, radish
x1 Cup of Milk
2. To fix the imbalance(quite a few people deal with this) spend a little time re-building but remember to let it rest as well.
3. Best advice you be STICK with it, I love what I do and its really a change of life. Do NOT get down because people are farther than you in skill level, use that to keep yourself positive and you can go far if you believe in yourself, we all start somewhere.
Best of luck to you man! Let me know how it goes, if you want to get into MMA than taking some sort of striking(such as Boxing, Muy Thai, tang soo do etc) would be a good idea and possibly if you can wrestling. Again best of luck and if you need ANYTHING at all, do not hesitate to ask, I will be more than willing to help