Most people start with one or two UNO's just to learn the programming language and to play with it. Two are needed to let them talk to each other , create master slave architectures and of course to have a spare one.
You cannot program an Arduino in labview AFAIK, but you can let it communicate with lab view over serial lines and let labview do processing or control the Arduino remotely. ON the forum are many threads about labview.
I would like to measure temperature and pressure and monitor them to my PC
What hardware do you suggest?
The most basic place to start would be to get an arduino and your sensors and have them send the data to the serial monitor included in the arduino IDE. Once you get that working, you can move to more involved formats.