is all you get at the start of the game is 3 horses?
what would be the right way to do this sell them or keep them?

Well Laparooze, play the game for a season or two untill you get the feeling on how the game plays, and after that you will pick up a few hints to do with what the game is all about, and if you still have any questions, just post on here and someone will be more then happy to help you mate, good luck and welcome to the forum

You only get 3 on the Normal mode. On easy, however you get 5 horses and on Hard you get 2 horses. Obviously it's up to you. You could get more money to buy facilities/better horses or keep them and see what they might do. I'd always sell them unless I had one rated 96+.

Also use the search button on the top of the page, there is loads of information on this site, hopefully you might find some more answers there. Hope that helps a little.