Your wheels will be fine either way.
Are straight 14 gauge (2mm) good enough? Yes, certainly, if good quality.
Are double butted better? Yes, lighter and result in a slightly more durable wheel.
It's up to you but if you are on a budget go 2mm.
This is not going to be your last set of wheels. In the future when you're on a bigger budget build a set of light weight "racing" wheels.

Al