Not nearly. The main problem is that it's a manual-focus lens, which will be very hard for a beginner to come to grips with for action/sport photography. (It's also a slow lens—it has a relatively small maximum aperture—so you would have to use lower shutter speeds or higher ISO settings, and it probably won't work well with automatic exposure. The lens is converted from a Practika mount; it wasn't designed for Canon cameras.) A proficient photographer who had learned the craft in the pre-auto-everything days could probably learn to use it quickly; a beginner will have a long struggle ahead. You have to learn how to focus where the action will be before the horse gets there, and press the shutter button just ahead of time so that the horse will be in focus just as the shutter actually opens.

I wouldn't get too wrapped up in the 7D part. It's a very nice camera and all, but you can easily get by with a 60D or a 650D and apply some of the price difference towards a more appropriate lens. The lens is much more important than the body at this stage; you can always upgrade the body later if your venture results in significant income, but it will be very hard to generate income if you compromise too much on the lens.

The Canon 70-200mm/2.8 is an expensive lens. When shooting sport, you don't really need IS (image stabilisation), so you can look for an older non-IS lens. And don't overlook the also-recommended 70-200mm/4—you might not be able to use a teleconverter, and it won't focus as quickly, but it is a good lens. You can also look at third-party lenses from Sigma and Tamron, but try to stick to the autofocus f/2.8 versions (the f/4-5.6 variable-aperture versions are really not that good for your pictures).