Should I be worried if my 8-month old is overweight?

Ask pediatrician . Without details as to how much your child actually weighs, i can't give a specific answer. However, your child's pediatrician can after seeing, evaluating, weighing and measuring your child. Make an appointment. Many new parents tend to worry unnecessarily about their children, and they need specific information and guidance from their child's pediatrician. They are there to guide you.
It is not a good idea to give a baby this age a bottle every times he cries. It may be that he is simply bored. Have a variety of activities he and you can play at home and ensure he is physically active. If he is eating solids, make sure you are giving him at least 5 servings of fruits and veggies and avoid sugary drinks and desserts.
No. It all depends. The first thing is to check with your doctor to make sure. Many breast fed infants are seemingly overweight but they seem to "slim down" once they are weaned. On the other hand some infants that are really overweight, tend to be overweight adults. Ensure your baby is active and is allowed mobility. Avoid giving empty calories via sugary drinks, offer water instead. Wean to a cup.
Yes. ...If the infant belongs to 'obese' category. It's been well known that an obese child/adolescent is at much higher risk to become an obese adult. Obese infants and toddlers are also at higher risk according to recent studies.
No. Usually, one need not worry if an 8 month baby is "overweight". Overweight means heavier than normal but not huge, which would be called "obese". At each check-up, the doctor will look at the weights and lengths on the growth chart for the baby. If the baby is gaining too much weight too fast, the doctor will review the diet and make the necessary changes, so the baby can grow at a normal rate.