1st approach - I think I understand your logic... just so it doesn't screw up your certification process.

2nd approach - sounds interesting.  I agree with keeping an experimental plot small.

Equipment purchase - think about this..... what equipment will you use most often?  A combine will only be used on the wheat crop - not on the hay crop.  The fertilizer spreader might be used on the wheat crop, and maybe sometime on the hay crop?  Likewise, the drill will be used to seed the wheat, and also the hay crop(?). So, I would think that having the fertilizer spreader and the drill will pay for themselves faster than the combine.

Also, if you were more of a conventional farmer, I would say that the sprayer will pay for itself more quickly as well.  However, depending on how much you will have as organic vs. non-organic, that may or may not be true in your situation. 

The other thought to keep in mind is your labor.... it does no good to have equipment if you don't have time to run it.  It may not be true in your situation, but there might be situations where you just don't have time to get every thing done.  That is where you need to custom hire.  Think thru your labor situation, and sit if you are okay along those lines.  Just a thought I had.