L.,
I don't know what kind of street you live on. I live on a cul-de-sac so I don't have to worry about traffic, etc. if you live on a 'street' and plan on closing that street to traffic? I would ask the police department if there is a permit that is required or something they can do to help you block traffic.
Our block parties are "simple" - it's pot luck style. My husband and I bring our BBQ'er from the back deck down and put it at the end. We have two canopy/gazebos that we use as well.
We are the block captains so we "lead" this. I am the POC. I send e-mails out to everyone and we set up the date and time. I coordinate the meals - making sure we are balanced and have a little bit of everything....just make sure that people know what others are bringing so that you don't have all desserts and no salads, etc.
Don't forget the condiments, napkins, utensils and plates....keep them in sturdy container so they don't get toppled or blown away.
Assign someone to BBQ duties.
Assign someone to kid duties - like a babysitter - so that people can enjoy and relax.
We bring out our "boom box". I spray the YARD GUARD an hour before the party so we cut down on bugs, etc.
When we had a lot of kids on the block - we had a bean bag toss, a small pool to cool off in, hoola-hoops and bikes....we tried not to give too much so that the kids aren't overwhelmed with too much to do. We have had a bouncy house (that was expensive - but everyone with kids contributed) and it was set up in the grass in the common area.