Recommended membership/ecommerce plugin?

I have two sites I am currently making. I’ve been trying to find a good plugin for membership/ecommerce utilities. It’s been a bit daunting. There are just so many out there and it’s hard for a newbie to really distinguish features with respect to cost benefit. A lot of the terminology is new to me and since most I need to pay for, I am a bit hesitant to commit right away.

What I need: Paid membership registration: forum/specific page access (integrated into website, ie no routing to paypal page for purchase), Accept paypal mastercard visa, shopping cart and integrated checkout, customizable look (editable CSS, no set skins), Decent user manuals/tutorials are also a plus given my obvious lack of expertise.

Any advice on which plugins would be best for this purpose based on cost, usability, etc I would really appreciate it. Sorry for my ignorance!