You definitely need to get that horse checked out before you "take them for free" because you don't know what they need. They could be insulin resistant or allergic or suffer from some kind of lameness.
You also need to be able to financially afford to have your horse seen by a farrier every 4-6 weeks, a vet at least twice a year with some money set aside for emergencies, and either board them or if you have them on your hand.. enough money to feed them properly.
They take a lot of work too if you plan on riding. You should be able to afford a trainer if you need one (which sometimes you may) and lessons because even the most accomplished rider takes lessons.
"Strength is the ability to use a muscle without tension"