DIY replacement of DVD drive with an SSD?
Two sites that are very Mac friendly are the iFixit site and the OWC (Other World Computing) site. OWC sells SSDs and many other Mac upgrades. I suggest you search the site for what you are looking for.

An iFixit example guide how to install a second HDD/SSD (with links where to buy all required parts and tools):

Installing MacBook Pro 15" Unibody Late 2011 Dual Hard Drive