You'll get lots of advice/help/opinions.

My $0.02:
The Platinum seating is pricey but worth every dime as it has shade which can be a precious commodity at the Vegas track. But any seat on the pit side of is a good one. This is easily my favorite facility on the circuit, it's clean, efficient, well managed, and comfortable. They know how to get 30,000 people in and out remarkably well.
As for getting there, there are city buses that make the trip in and out, but I've heard from a number of people that it is a hassle and doesn't work very well (hard to get there, confusing to get out, etc.). I always rent a car, it's a city with a bazillion rentals and prices are good. The most direct route is just to take I-15 north out of town until you get there, but it's always torn up so traffic can be terrible. I usually find my way to N. Las Vegas Blvd. and come in the back door. Don't try to do the taxi thing - you'll get there just fine, but getting a taxi back will be a nightmare.
As I said, this is my favorite track, Bruton Smith knows how to run a race track, at least from a fan's perspective. Paved pits, lots of food choices, easy and free parking, smooth traffic in/out, etc. You'll love it, and it's a great choice for newbies.
Hope this helps,
Chris