Hi John,
3.1 is a very good option, I suppose. If you have enough space in your room, that is. You will hear plenty of bass with a subwoofer, but how helpful it will be in a small room (for mixing) is not a given. But there's no question, if you care about bass below 60Hz, you need a sub.
Foam, yes. Stuff from Universal Acoustics is reasonably priced and works well. It also doesn't smell when unpacked, which is nice. Pluto-1 is a good starter kit. Use it to diffuse direct reflections fro the speakers.
Bass traps - yes. Can't give the exact recommendation here. If you are adventurous, you could make them yourself following the advice here. Set them up in the corners, as many people suggest.
Acoustic measurements... maybe, but that's after the previous two points. You will get used to the new room, and after some time you will actually know what needs a correction (with some luck). Not precisely, of course, and that's where the measurements will come in handy. But the other way around... I'm not so sure. It's the same principle as with mixing in general - don't do something unless you know why you need to.
Cheers,
Crusoe.