If I am overweight, will I be able to see my baby's heartbeat?

Yes most likely. Depending on how overweight you are - finding the baby's heartbeat may be more difficult; however even in morbidly obese women- doctors are able to locate the fetal heartbeat. It may be harder to detect on non-medical devices such as the home purchased items - but medical professionals should be able to locate it without too much problem. Talk to your doctor about healthy weight gain.
Yes. Increased abdominal fat can make ultrasound more difficult, but with today's technology we can still scan all but the most morbidly obese patients. Monitoring during labor can be more difficult in very overweight women.