Some features you want to look for in a Mig welder are adjustability of the wire speed and the heat range. Most cheaper machines only have 2 settings - low and hi switches for either adjustment; better machines have rotary knobs for more fine adjustments. You also want to consider the availability of the consumables for a given machine, like tips, gas shield, etc. Foreign made stuff may require one-off, hard to get replacements - more common makes are easier to get consumables for.

Settle on the kind of welding you think you'll be doing the more of, and the power source you have available to you. 220 volt may require some electrical wiring to install the proper plug. Anything more than 1/4" thick steel will require a good 220 welder. Having said that, I have two machines, a 220 and a 110, and 95% of the welding I do I use the 110 machine - Sheet metal and up to 1/4" inch. Stay away from flux core machines. Everything you described in your things to weld could be done with a 110 machine of sufficient amperage. My 110 machine on its highest setting is 100 amps. if you have 220 volts available I'd get a 220 volt machine with good adjustments - then you're covered if you decide to step up to welding heavier stuff.