As far as some of your questions.
No brand is "Better" than the next. They all have good and bad characteristics. Pick your poison, so to speak. You talk to a Trek guy, he'll say Trek is the best.....or a Specialized guy, you'll get the same answer. My suggestion to you in this regard is RIDE LOTS OF BIKES! The one that works will make itself known. As far as components, you have opened a can of worms. Given you budget, I would suggest Shimano. Excellent equipment for a reasonable price. I wouldn't drop below 105's myself but I know others that say Tiagra work just fine.
Best of luck to you. I hope this helped a little.