The key to travel in your scenario will be to move quietly enough to avoid the zombies, and to find places to camp that are defensible. If you are quiet there will be zero or only a few zombies in earshot. You will need to stand watch at night, and you will need to guard the horses. Camping near natural noise sources (waterfalls, rapids, wind in the trees) and in places that naturally absorb sound (dense forest, box canyons, steep ravines, caves) will have merit. Given the general uncoordination of zombies, rough terrain may be more to your advantage. Most of the above have risks of being trapped too. Perfect campsites are going to be hard to find.
Find air powered rifles. Some were used in WWII as sneak weapons. Not as powerful as a conventional rifle but still deadly, and much much quieter. If one or more of your members has any skill with a bow, raid archery shops for arrows, although a head shot will be tricky. Crossbows are another fairly quiet option.
Build proper silencers for conventional rifles. A silencer doesn't make a weapon silent, but it reduces the noise by a lot. Instead of attracting every zombie within a mile, you may only get noticed by ones within 300 yards. Silencers make the rifle heavier, change it's balance, and interfere with the sighting picture. A good silencer is likely to be the size of a can of tennis balls.
Noise makers. Having units that can be set with a delay and then make a lot of noise for a few minutes may be the trick to getting away. Such devices should be rugged, and have timers for how long to make noise. Some may be programmable to turn on and off repeatedly.
Poisons. Stop by a gold mine and get bulk cyanide. Zombies have some sort of metabolism. Cyanide binds to hemoglobin rendering the blood supply useless. A dead horse slathered with a paste of cyanide may kill off the immediate crowd.
Gasoline flame bombs -- set as booby traps. Quarter stick of dynamite in a milk jug full of gasoline might ruin a zombies day.
snares. That shuffling pace lends itself to snares. Part of your defence perimeter is lines with slip loops a couple inches above the ground. It won't kill them, but it you catch them they have to take time to untangle themselves. Given the number of missing fingers this will take time. Following zombies will trip and fall over the snared ones. The effect will be to smear a mass attack over time, allow you shotgun reloading time between waves.
Programmable noisemakers may be used to wear out a bunch of zombies. Set up two 500 meters apart. One goes off for 5 minutes. Zombies stream toward it. 5 minute silence. Zombies start to disburse. 2nd one goes off, zombies stream toward it. With the right spacing and timing, you can keep them sloshing back and forth like a wave in a kiddy pool. Eventually they run out of energy.
Having one or more zombie dogs will be useful. These are dogs that are trained to detect the faint trace of the undead that they leave behind. The dog is trained to figure out which way the zombie was traveling, and silently indicates which way.
If zombies have need of water, then traveling sections of land that are dry for miles may be effective. Load up on enough water for a night when you can, and camp on a dry ridgeline. This may allow a much smaller watch to be kept and give everyone more time to rest.
This will require extra horses. Water is heavy. You will need several gallons of water per horse.