Do I need a merchant account from my bank to accept credit cards on my online store?

You need one from some place. PayPal has their own. If you use them, you do not need one.

Paypal is a decent temporary solution but if you want to trigger more impulse buying and ease of checkout you should probably get a merchant account. They aren’t very expensive if you do your research and find a good company. DON’T TRUST SALES REPS, they are only looking out for themselves. Make sure you talk to someone who has some experience and you best interest in mind.