When I was first testing out my DIY laser cutter, I used a 445nm diode. It could cut paper and engrave wood, but that was about it's limits. A 40W tube will cut 6mm acrylic OK, but pretty slowly. My tube is rated at 50W (but I have no way of testing), and I can cut 6mm fairly cleanly at around 6mm/s, while for 3mm acrylic I can go about 10mm/s.
Air assist is a must, and whatever you do, don't try cutting PVC! And yes, venting is an absolute must. I made the mistake of trying to cut ABS before researching, it melted and even with exhaust, the tiny bit that leaked into my garage gave me a nasty headache for over an hour. I later discovered I was breathing hydrogen cyanide - lovely!
Do lots and lots of research, there's plenty of info out there