Landscaping - Do I Need a Backflow Valve for Hose-Sprinkler?

We're re-landscaping a 40' x 40' backyard in San Diego that was totally neglected by the previous owner. We'd like to put in a small (20' x 30') lawn area for our kids, a play area with a swing and a sandbox, and two rows of vegetable garden, and plant shrubs and ground cover for the remaining areas. We can't afford an in-ground sprinkler system, so I was going to just attach one of these faucet manifolds ...
http://www.homedepot.com/catalog/productImages/300/72/72f01403-f292-4af7-9994-f350fe16770e_300.jpg
... to our backyard exterior faucet, and make an above-ground sprinkler system with 3 different zones. Each of the 3 zones would be fed by a garden hose with a battery-operated timer. One of the 3 would be a sprinkler for the lawn. A second would be for the vegetable garden, and the third for a drip hose for the shrubs and ground cover. The 4th valve would be for a garden hose for manual hose use.

My question is, do I need to attach a back-flow preventer valve in my set-up? If so, can I attach one just at the top of the manifold? Or do I need one for each of the 3 manifold outlet valves connected to a sprinker or drip hose? Is there one you recommend?

Also, do you see any problems with what I'm planning to do?

Thanks.

One between faucet and manifold is fine. First, check your faucet. It may already be an anti syphon type.

One between faucet and manifold is fine. First, check your faucet. It may already be an anti syphon type.

How would I identify it? It looks like a very simple bronze hose bibb. Looks like this:
http://www.homedepot.com/catalog/productImages/300/b7/b7cc85c3-884f-419c-ad79-3034599fe640_300.jpg
The house was built in the 70's.