Life long horse owner here.
It sounds like you have thought this through. But I am going to give you more to think about.
FREE board is great this may or may not work out. Things change. Farms sell. People die. There are droughts. In either event, don't count on this for the long haul. Horses can live for a LONG time.
I have a horse right now who is 37 years old. Now, let's say 25 years ago if someone pointed to all of my horses and asked "which horse do you think will still be with you in 25 years?" He would have been the LAST one I would have pointed to. He was the oldest at the time. The one who had been the most beaten up. The one who had the most poor health, the most vet bills, the hardest to feed, the one who got hurt the most, the worst feet, you name it, he had the problem.
The most healthy, with the least problems and the youngest have been long dead. Sudden death by aortic rupture. Go figure.
As for choosing a horse. I have almost 50 years of experience raising, breeding, riding and showing. And I STILL take a professional trainer with me when I am buying a horse. Why? Because she knows what I am looking for withOUT the emotion. And she can see through the bullshit. There are SO MANY HORSES out there. Don't settle for a horse that is almost this or almost that and only needs a little of this or that. WAIT and get exactly what you want. It's out there. Believe me.
I have GIVEN AWAY horses that only 5 years ago would have fetched $10,000 or better. So, wait it out. Don't settle for someone else's problem horse who may hurt you.
I had free board too. Big fight in the family. If I was getting something, everyone else should too. Blah, blah. Guess who got the boot? Me.
The other thing to consider is pasture. Even though you plan on pasturing your horses, not ALL horses can tolerate fresh pasture 24/7. They require a rotation schedule or they will founder. I have three horses who can only tolerate 2-3 hours a day in the spring on pasture. After it dries a little, they are ok. But that early lush pasture is a big no-no.
And hay. This year it's a feast. There is hay everywhere. But the last few years hay was scarce and was selling at a premium. Decent, not good horse grade alfalfa was selling for $12.00-14.00 a small square bale. And much of that you had to throw away because of mold. You couldn't get the premium horse quality alfalfa because it just wasn't available.
With all of that being said, and I were you....I would do it in a minute. My horses are my life-blood and can't imagine life without them.
Since my days of free board with family, etc. we now have our own place. It's nice not to have to ask permission about every little thing before you move a gate or a piece baling wire.
And if I were in my 30's again? I wouldn't even think twice!!
For tack and other accessories, go on Craigslist. There is a horse person selling out every day. There are unbelievable bargains on there all the time. I have seen good as new stalls being sold for less than 1/2 price. You go tear them down. You're young! Go for it!
[This message edited by sadtoo at 12:37 PM, July 12th (Friday)]