That's what I did when I was faced with a similar situation. Worked a treat. Even a really cheap arc set, while not being that easy to use, should do the job you need it to.
That really depends on how tall you are. My workbench is around 900mm high (just under 3', I think) and I'm about 5'9". I find it's about right. Try and mark the height on a wall somewhere and see if you'll be comfortable with it. Nothing worse than trying to weld when you're not comfortable!
I'm not sure. When I went to start, it would go for maybe half a second, then cut out. The light on the power switch stayed on, but there wasn't enough current on the wire to arc and the wire feed wouldn't go at all. I just took it back and told them to replace it, so I never found out what...
My mig is a rebadged Kende machine. While it's not as terrible as it could be for the price, the first one I had self destructed after 3 weeks. Save yourself the frustration and avoid the things.
I've found that 0.9mm gasless wire runs very well through a 0.8mm drive roller. Better than it did going through a 0.8mm drive roller. In fact, since accidentally buying 0.9mm wire, I haven't had a single problem with wire feed. This is on an el cheapo chinese made machine though, so YMMV.
All of these make my incidents seem rather minor. The most recent one (just last night) gave me rather a fright than anything serious. I got my hands on an incredibly cheap briggs and stratton motor in the weekend, perfectly suitable for my next project. Given the price, of course it wasn't...
How much wire did you go through to build something up that thick? And if you don't mind me asking, what temperature did you have it cool to before cleaning it up and doing the second pass?