Congratulations on the new rack!
There are quite a few home gym threads on the forum. If you enter these terms into a google search you should get a lot of useful info:
home gym site:startingstrength.com
garage gym site:startingstrength.com
Here's a good thread to start with: http://startingstrength.com/resource...rage-gyms.html
Barbell - lots of people like the Rogue Ohio Power Bar if you're not doing olympic lifts. Here's a thread about barbells: http://startingstrength.com/resource...ells-ones.html
Bumper plates will help protect your garage floor if you'll be deadlifting heavy without a platform. 3/4" horse stall mats from tractor supply would be something sturdy to lay down on the floor that you could still park on (or move out of the way...though a 4'x6' size weighs about 100 pounds). You could make some kind of platform that you could disassemble and move out of the way as well. Hopefully your garage floor is flat and level. Of course the downside the bumpers is the cost and - unless you splurge for competition bumpers - the amount of loadable sleeve length they take up.
These spotter arms are available for the wall mounted rack: Set of Safety Spotter Arms - Weight Training Safety - Rogue Fitness
The Rogue flat bench is sweet.