First; who owns the hay? In a lot of rural development, you may have bought the land, but the current crop is owned by whomever is farming it.

It is better to strip the topsoil and get to undisturbed earth right before construction. Otherwise you'll deal with runoff and a muddy mess. And if you don't have silt / catchment fencing up - you could end up being fined.

You could get a soil test after you reach undisturbed soils to be confident that you were building on stable soil. But I would not "open" the site until you were ready.

The ONLY advantage of doing it early is that you'd find problems earlier and PERHAPS be able to address them - but still not worth it, IMO.

Foundation problems are caused by inconsistancies in the soil surrounding the foundation that allow the soil to expand/contract due to moisture/soil movement or simple earth movement.

That means the soil compaction/type/foundation footings are the most important steps in pouring a stable foundation.

As the prior posters have said, digging long before construction is generally a bad idea. But, insuring the proper soil conditions after excavation is more important.

It is also improbable to think the foundation will never have a problem. Our current house, built in 1965, experienced two long cracks in the foundation two years ago(previously uncracked) due to several years of minimal rain and then two years of excess rain. The clay soil simply moved, no way to prevent it from happening.

Even in areas not known for catastrophic earthquakes, such as central Ontario, quakes are the suspected cause of cracked basement floors and even foundations. Frost quakes (cryoseism) and adhesion freezing, can also damage foundations.

No. There are no advantages in putting a foundation in place and waiting an extended period for commencing the rest of the construction.

Quite the contrary, as many posters above have pointed out.

Do it once and do it all together in a proper and managed construction process.