1. It benefits the environment, prevents you from eating hormone, antibiotic, or steroid injected meat, the fewer animal products in the diet, the less saturated fat and cholesterol the diet usually contains= decreased rates of coronary artery disease in vegetarians compared to nonvegetarians. Vegetarian diets are rich in fiber, phytochemicals, and health-supporting nutrients. Fiber-rich vegetarian foods help prevent constipation, hemorrhoids, varicose veins, and diverticulosis. Fruit, grain, and vegetable rich vegetarian diets are also high in beneficial vitamins, minerals, and phytochemicals such as vitamins E and C, which promote and protect your health when you get them naturally from whole foods. Vegetarians are healthier, slimmer, and also have lower low-density lipoprotein cholesterol levels, lower blood pressure, lower overall cancer rates, and lower rates of type 2 diabetes. (etc.)
1b. Negative side effects...I don't know if everyone is like this but I used to get sick a lot. But that's probably because I don't eat healthy enough and wasn't sleeping enough.
2. Like by-products? You should check out the peta website, that's where I get information from. Read the food label...one ingredient you should look out for is gelatin...gross. Another common one is chicken powder or stock. And if you like asian foods, google ingredients to make sure you're not eating fish.
3. The only thing I found difficult was chicken, I still think it smells good and it still makes me hungry when I smell it. But I've been vegetarian 4 years, so it's easy for me.
4. Don't think so..? Google and PETA are my best friends when it comes to all things vegetarian/vegan.