I'm just a newbe here myself.
Hopefully the pros will chime in, but heres my 2 cents.

1. What is the benefit for more zones?
   More zones should allow you to have more heads for better/efficient coverage. But you didn't mention how many heads they were planning?

2. Is anyone use those contractors bofore?
   Not me.

3. Each zone should have a valve go with it, right? Yes.

4. Any details I need to pay attention?
   Make sure you have coverage in the areas you want.

The water line connection should be made at the water meter.

If you're not on city water, you may have issues with water pressure. Be sure they test your water pressure.

Be sure the installers show you how to adjust the heads. They may require some tweeks after they leave. Also, while the system is running inspect the valve box for leaks before they leave.

If there any areas you don't want the water lines to run, make sure they know about it. e.g. future planting bed, patio, etc.

Understand your warranty.

Hope this helps.
-jasper

Jasper:

Thank you for the answers. Yes, need to understand the warranty. If the coverage area is same, then I guess no need for more zones.

Ordinarily, the more zones you have the more flexibility you have in programming. I would recommend that your zones are hydrozoned. Meaning that you would water like areas together based on sun exposure, soil and plant types, slope ect. The drawback of having more zones is that your watering window expands and there can be excessive pressure causing misting, which wastes water. You should have a rain/freeze protector installed on the system as they are inexpensive and conserve water.

All Wet
Texas Licensed Irrigator #1897 since 1984