1) How deep should I dig my trenches for my lateral lines? I live in
the Seattle area; I'm not sure how much of an issue freezing is.

2) I notice that sprinkler head bodies come in varying heights. I'm
just going to be watering a 350 sq. ft. lawn (no shrubs) and I'm
wondering what height I should purchase? All of my radii are 10' or
less.

3) Double-check valves seem to be sized to fit a range of sizes. I'm
considering the following Conbraco unit; will it accomodate my 1-1/4"
PVC mainline?
http://www.sprinklerwarehouse.com/1-...c40-105-t2.htm

4) I had a plumber tell me that I could bury my double check valve in
a valve box underground. All of the models I see online, however,
seem to require them to be mounted a foot above the ground. Are there
types that can be buried? I don't mind putting forth a little extra
money/effort to protect my potable water.

5) Can someone recommend a Seattle-area retailer that carries
sprinkler heads, valves, and accessories that are of higher quality
than one finds at Home Depot?

Thanks for any guidance!