My advice is to start slow adding in meat to your diet let your body adjust. My long time vegetarian husband just started adding chicken to his diet last month & he always has a few meat-free days a week or he starts to feel heavy & gross. So try easing into it.
Also, since compassion for animals is an issue for you, try sticking to free range & organic animal products. They're better for you (omega 3 vs. omega 6 ratios), they're better for the environment & they're kinder to the animals. And good on you for having a kind heart.
You ask if you ONLY eat meat, veggies, fruit, creatine & protein shakes, will you be doing good or bad? Well, I think that depends on getting good quality food, in a wide variety. Are you eating grains now? Whole grains? Steel cut oatmeal is also great for you, as are beans (though you probably included those in your veggies I guess).
Somewhere in this site there's an article by TC, I think its called The Magic 13 about the best foods you can eat to support your goals. Do a search. Also Berardi's article's are very informative - especially his 7 Habits article. When I started to eat according to the 7 Habits - all 7 of them! - I lost 35 pounds.
And boxing rocks, by the way. Good luck!