Everything that the horse is expected to do at an event or trek should be tried first in a safe environment. We shoot around our animals at regular intervals. We ride them over rough country, ford creeks and rivers, and expose them to heavy traffic. We especially work them heavily the week before a trek. Still we have occasional surprises. Training should include the rider unless the trek is specifically a training trek in a controlled environment. I would rather have beginners in the woods near our farm than on the Big South Fork where animal or human medical attention or other help may be hours away.
Horses today are just not used enough to keep them in shape. Generally, horses in pasture get much better exercise than those who spend their lives in stalls but a regular program of riding is still the best. On a trek two years ago, we covered thirty six miles over fairly rough country in two days. Four of the six horses were exhausted by the time we got in. No one was hurt but in my mind that was too much. On the other hand Deanna and I covered twenty one miles one day over similar terrain last August with a couple of our favorite horses and a pack horse in tow, and they were still full of bounce. In one wagon train that we were a part of in South Dakota, after twenty five miles on a hot day, three horses had colic. Distance depends upon the horse. The rider needs to be conditioned too. On a typical trek we walk as much as we ride and the ups and downs are constant. People should remember that the calorie burn for riding is the same as that for walking.
There are a number of options when it comes to tack. Probably the best advice is keep it simple. English saddles are very proper for the period and most types, such as jumpers, dressage and general purpose saddles were already invented. Plantation saddles, hell hounds and a variety of home made rigs were present too. Most frontiersmen covered their saddles with blankets or hides and this, besides making for a more comfortable seat, covers the sins of modern tack. A good recreated eighteenth century saddle may be better but might be more common under a Tidewater planter than a longhunter. A folded blanket or deer hide goes under the saddle. Most headstalls were simple affairs just a strap running back from the bit around the horses head with a brow band. I would recommend selecting the bit more to match the horse and rider than for historical accuracy. There were probably more straight snaffle bits (a bar with rings on each end) on the frontier than anything else, but this may not give an inexperienced rider the control needed. Halters were of rope or leather and generally "A" shaped (a loop around the horses neck and another around the nose connected by a ring on the bottom and two cheek straps). On the trail the halter and lead rope should be left on. Other tack might include a wallet (a closed sack with a slit opening) or saddle bags, hoof pick, hoof knife, nippers and a first aid kit for both man and horse.