Being plus-size can to some degree potentially affect ultrasounds, fundal measurements, hearing the fetal heartbeat, and feeling your baby move — but these are not big problems to worry about.
With a fetal heartbeat, I've found that sometimes a plus-size woman's pregnancy needs to be a bit further along, in terms of weeks, before I can hear her baby's heartbeat. But then again, I've had the same experience with thin patients. Of course, it also depends on how good your healthcare provider's hearing is — my nurse practitioner can usually hear the heartbeat before I can! I resort to an ultrasound machine relatively quickly if I don't hear the heartbeat in the first few minutes. As your pregnancy progresses, it will be easier to hear your baby's heartbeat.
As for feeling your baby move, some plus-size women do feel fetal movement later, but other factors are involved — such as whether it's your first pregnancy or whether the placenta is positioned in such a way that it's cushioning the baby's movement. So no one can say for sure whether the delayed perception of fetal movement is because of your being plus-size.
None of these are issues to sweat about. Every woman's pregnancy is different, no matter what her size, so don't let these concerns make you anxious.