PayPal and MarketPress

Hi I'm making a website for a small business for a client and is at the moment setting up the shop page. I'm very new in web design and I tried to find other posts with the same subject but could not find any, if there are I apologize.

On the site I want the customers to be able to pay through paypal on the site, PayPal Express Checkout. I have not set up a PayPal account yet, with PayPal Business there are three categories, Standard, advanced and pro. To use Express checkout is it enough with standard or do I need to get either advanced or pro? Also I want to use marketpress shopping cart function. Is it possible also with just standard PayPal?

Also after I got a paypal account I'm suppose to get PayPal sandbox right?

Thank you for the help I appreciate it