So if you're just learning I would highly recommend not starting with nippers! They take some practice to use well and you can take off a lot of foot really fast and therefore do more damage more easily. I find when people are learning to trim, the rasp is perfect, they get tired before they could possibly hurt their horse.
So it's a good safety net. If you find that the feet are too hard to make any headway with the rough side of a sharp rasp, then wait for wet weather or use the fine side. That will make it a lot easier to get something off the foot with the rasp. But again, I wouldn't just start randomly rasping on their feet until you can get a bit of instruction, with the exception of rounding off an obvious chip or some such.
It's doubtful that your horses will wear their feet enough in the track system that they won't need to be trimmed, unless the track is on decomposed granite or some very abrasive surface. Even then - they don't generally wear them evenly and will still need to be balanced and maintained. We just don't have the kind of footing here in the US that really lends itself to self-maintaining feet unless the horses are traveling many many miles a day.
You shouldn't need to go to farrier school to learn to trim - you may be able to find someone locally who can show you, or attend a clinic or two. There are some good options out there.
