Have some questions about WP

Hello BHW. I have a few questions about Word Press. I'm wanting to create an e-commerce site, with a member login. Is this hard to do with word press? If I have a e-commerce theme, are there any additional costs attached to selling products online? Also as far as member logins go, can you create one with a plugin or something?

Thank you!

You should probably look at Magento, PrestaShop, and the other eCom CMS