Don't go to the welding shop for advice. It's like asking a used car salesman what kind of car you should buy. Most people who work in welding supply stores have limited welding experience.
Do not buy gas-fired welders. They cost three times as much, not to mention the cumulative cost of fuel and maintenance. Buy this plugin. If you need to hire an electrician to give you a 220V socket.
Stick to brand equipment. ESAB, hot arc/fire, miller, Lincoln electric, or hobart. No other brand is worth your money or time. Remember that what you get is what you give.
For bonding, you need at least 150 amps output. Traditional transformer welders are the way to go. Inverter-type welders may be smaller and lighter, but they won't last long and the cost of fixing them is too high.
You test the welding machine with welding. Get some different rod thickness and see how good it is for each one. The most important thing is to listen to the sound of an arc in your ear. You want to hear a smooth, soft, crackling sound. You should also pay attention to the amount of splashing.
