...PS: where can I find codes/regulations regarding sprinkler systems, components like what kind of backflow preventers to use etc.
Call your local Building Safety Department. They should be able to tell you what building codes apply to your area, and possibly even answer questions such as what type of backflow is required in your area for irrigation. Don't be suprised if you discover a building permit is required (often is when ever you are modifing any plumbing/electrical/natural gas/sewage other than replacing a fixture).
The laws, permit requirements, and permit costs vary greatly from city to city. Some will require a certified plumber to make these sorts of connections. Some will allow any industry standard backflow preventer, some will be so restrictive as to codify a part number.