Yeah, this is a good topic because of that damn hindsight thing!
I already listed the one thing about the overhead crane or engine hoist, but on another more practical note. I got my airplane in the air in 3 years from knowing nothing about airplanes to choosing a kit, building (not a quickbuild), designing and building an alternative engine FWF to first flight, then learning to fly.
It was all great fun at home in my shop where I could work on it every spare minute. There was many very late nights where the creativity was coming fast and furious and lots of times I'd wake up in the middle of the night with a great idea and head to the shop.
Then I was in a hurry to move it to the airport. I hated working on it out there. I could go on with a long list of reasons why, but it was hard to continue experimenting with it out there and I started regretting doing some things that I was otherwise glad that I tried. I tried to deny this to myself and stay excited and positive about it all.
By the time that I took it home 2 years later, I was not really interested in dealing with it. And since we had just bought the land across the road, I had a new shop to build, barns to build, a kid to raise and a thousand other distractions, so that it took till now to get interested again.
Fortunately, my wife only once made mention of selling it, but from my reaction never mentioned it again, but I can see how so many projects get abandoned at this point.
So from that, what would I do differently? Hard to be sure since I didn't have the flight experience to make some different choices, but even an extra year in the shop going at a little slower pace wouldn't have hurt. That old saying about if you don't have time to do it right the first time, then when are you going to find time to do it the second time, is even harder when you are no longer in your well equipped shop while doing it the second time. Now it's not like the workmanship is bad, when I say about doing it right, but rather if some of our design choices are constrained by the amount of work involved. Now I would rather do an almost unreasonable amount of work in the comfort of my shop than almost anything in the field. I really enjoy building at home, but when it's not at home I just want to fly it.
Previously I would cling to questionable half-baked ideas because of the time and money that I'd invested in it. That's not to say that half-baked ideas are all bad, but now I'll be far more likely to move on and try something else regardless of time and money investment if I don't feel good about something.
So when you're considering something like relocating a cooler and are certain that it would improve performance but don't want to to do the work involved, just do it when you're still in a well equipped and convenient work space.
And all you lucky SOB's that have an airstrip and hangar at home, you can disregard this advice.
I could fill several more posts about more specific items that I'd do differently but this was really the big picture and once again it may seem obvious to many but that has been my experience.
Ps. I often get asked about how many hours are involved in building this plane. I just laugh and say I don't know or care. It doesn't matter.
George started us on a good topic. Building an airplane is an expensive and labor intensive process. I've made many decisions where I didn't really like something, but liked the prospect of the time and expense to change it even less. Those things don't tend to get as much coverage in discussions as what was actually done, even though there is a real lesson in what the person who just did something wishes they'd done differently.
This thread could be renamed "What I'd done differently"
Another good one would be "What I'd do again"