I would become a trainer, mostly because I would like to travel around and explore the world. I would also battle the Gym Leaders and try to enter the Pokemon League, but I wouldn't be bothered about winning it.
My other goal would be to get a Pikachu as my starter, not because Ash got one in the Anime, but because it was the first Pokemon I ever owned, both as a trading card (which was the first time I ever saw a Pokemon), and as my starter in Pokemon Yellow.
As for my other Pokemon, I't would depend on how the world was separated Pokemon wise, but if say America was one region, Japan was another ect, I would probably be like Ash and catch Pokemon native to those areas, and then start fresh in every region, unless I got an Eevee, that I would try to evolve into an Umbreon ASAP and would stay on my team all the time where ever I went. If however if the world was classed as just one region, I would only catch 6 Pokemon in my travels with Pikachu and Umbreon been two of them, the other 4 would be decided upon later.