Make your gates plenty wide! And driveways with plenty of room on both sides. Our own equipment has gotten larger over the past 30 years! In addition, we have also had a need to have lime spread (have to get the lime truck and spreader in), fescue combined (combines are wide!) weeds sprayed (co op sprayer is wide), not to mention disc and planter if you plan to do any row cropping or even to totally replant a pasture, will you be having your place hayed? most of the more modern rakes are harder to navigate through a small gate than an older side delivery rake. A tractor that can handle large round bales needs more gate room and turnaround space than if you are feeding squares with a small tractor or utv.
Gate and driveway placement! Will all the equipment/trucks that will be on your place in the future make it under that tree or electric line that you have running to your barn?
For a few sheep, things can be fairly small and simple but it amazes me the types of equipment we have had on our place!
As you get older, it is nice to have things set up for ease of use. We finally have gates that we don't have to pick up to open, they actually hang and swing The utv can be backed through the barn gate all the way to the feed bin for unloading. Alleys and chutes make things much easier.
Consider your dogs! Are you going to have any cattle? We just built a catch/working pen and one requirement was that there was enough space at the bottom of the fencing for a dog to get under. I would hate to loose a good dog to a mean cow just because he couldn't get away!
Portable is great at first, and remember even the permanent is changeable if it doesn't work for you in the future!
Good luck and have fun!