Newbie need guidance

Hello,
I use drupal for making sites and a client wanted me to use wordpress and I found it very easy as compared with drupal.

I like the time saved when making a blog in wordpress and would like to thank the people behind wordpress.

I would like to know how easy is it to make plug ins for word press and if its easy/possible to make web sites like ebay.com, amazon.com and elance.com

I am hoping for a clear picture as I am going to spend the rest of the next few months working with wordpress

Cheers,
Vishal