Its been almost 30 years since I bought my first wire machine. I used .030 and didn't try to weld anything less than 14 gauge until I got used to the machine. If you start on thinner stuff, you will burn holes and get frustrated. I have welders from 135 amp up to 440 amp, and each has a purpose. When I work with my jalopies, I use a 140 Hobart that runs on 110 with .025 wire and CO2 argon mix gas. However, I would recommend starting with some heavier metal so you can learn to watch the penetration. And make sure you use a lens that is light enough so you can watch what you are doing. I wouldn't even try to use flux core because it will frustrate you. Once you have lots of practice, you can use flux where there is a wind. I am assuming you bought the machine to do some work on your vehicle. Once you become proficient, you will probably not use anything but .025 wire. I still practice on scrap similar to what I am going to weld to get my machine set at the right heat and wire speed.
