4-6 months after groundbreaking. Here in South Dakota it's best to start as soon as the frost is out of the ground to buy as much time as possible before it gets cold again.
I would ask a local broker for what the building/land ratio should be in your area. My 30,000 sf building is on a 120,000 sf lot. Plenty of room for outside storage/truck parking.
If you use a submetering company you only have to install 1 meter from each utility company. Then as you add tenants, you can add submeters to break down the usage between suites. I'm sure it varies with electric companies, but locally it would have been $90/meter/month. Submetering is free after the purchase of the meter, unless you have them bill direct.
The sprinkler company you hire will need to do a pressure/flow test to design the system. If it is too low, you will need to spend more on bigger pipes or even a pump. Do this test during the due diligence period before closing on the land.
Yes I would contact an architect before buying the land.