Setting Up The Bass
An ERB is very much a different animal from a "normal" 4 string bass. The increased neck width, and possibly the length of the neck, make some of the usual adjustments a bit more tedious. Of course, intonation and action can be adjusted in a manner similar to any other bass, but a great deal will depend on your choice of bridge and the number of truss rods the bass has.
If you are uncomfortable with bridge and neck adjustments, you can try to reach out to a local bass technician and get the axe set up, just be aware that many (or most) local shops have little to no familiarity with ERB's.
Most retail shops do not sell 6+ string sets, so just popping into your local Guitar Center is going to be a futile effort ... you are much better off finding an on-line source and ordering that way. The very good news there is that the options are much better!
You'll have a greater selection with round wound strings than you will with flats. Currently, there are no manufacturers making a flatwound F#0 (gauge .165 or greater), and the higher end F3 and above (gauge .022 and thinner) are only single plain steel. There is some discussion that heavier gauge flatwounds may become available in the future, though.
Here are some good internet sources to locate strings for your ERB:
www.sitstrings.com
www.juststrings.com
www.conklinguitars.com
www.octave4plus.com
www.labella.com
JustStrings.com has by far the largest selection of manufacturers, but the web site takes a while to navigate. Octave4Plus.com is a relatively new company that speciializes in strings for ERB's and is one of the most likely to eventually offer up flatwound single and string sets. If you are having issues locating strings for your ERB, give me a contact and let's see if we can find what you're looking for.
ERB's offer a wider range of tonal options than 4 string basses, especially since the notes can go so much lower and higher. You'll want to consider what your performance needs are ... for example, if you do a lot of chording or tapping you might want to get an electronics package that will support cleaner, higher guitar-voiced playing.
Bass Bridges
Bass bridges are a bit of a pain in the butt to locate. Typically, many of the bass builders use custom made bridges for the basses, however, a pretty common bridge (for up to a 7 string bass) is the Hipshot. Hipshot makes three different types of stock bridges:
Hipshot Style A Bridge 
This is as close to an industry standard as you can get for an ERB bridge. The Hipshot A has adjustable saddles for each string and is top loading (meaning you don't need to slide the strings through a hole, which is cool when using thicker strings).
Hipshot Style B Bridge
Hipshot Individual Bridge
