The first thing you need to do, is lose your budget. I hate to say it, but if you want the ability to cut/weld up to 1/2" plate, it will not be cheap. It also will not be a quick project.
The first thing you should do is go talk to the local community college or trade school and see if they offer any welding classes. Learning from a professional will cut YEARS off of the learning curve. I have been welding for several years, and I still consider taking classes (if I could just find the time between paying the mortgage and working on my BSEE).
For equipment, go with name brand gear, plain and simple. Miller, Hobart, Lincoln are the big 3. My personal preference is Miller (btw, miller owns Hobart.....that is their "economy" brand...but still good machines). Lincolns are just as good, so it is a matter of features and color. If you want a MIG (very easy to learn on, compared to stick or TIG or oxy/acetelyne), you will need a machine that puts out 250 amps to get that 1/2" plate...so you are looking at ~$1700 if you watch for a good sale. You can buy attachements to make a mig weld aluminum pretty inexpensively (the spoolgun for my Millermatic 210 runs about $300, then I need to get a bottle of the mixed gas, reverse the polarity of the welder and I'm all set...easy process). The problem with MIG is that it doesn't leave nearly as nice of a weld as TIG. I only say this because you mention doing artwork. A TIG will give you infinately more control than a MIG, will give you a superior weld (astetically), and most TIG's will also double as a stick welder. The downside...a nice square wave TIG will run you 3x as much as a MIG. Consumables also cost more per foot of weld. A simple "buzz box", or stick welder is very inexpensive compared to a MIG or TIG, but they are difficult to learn on (again, take some classes, this will help you ALOT), don't give you as much control as a MIG or TIG (particularly when you are still learning), and generally splatter alot more, leaving a bigger mess to clean up. But the price is good, and they are very versatile...just buy the right electrode for the job, set the polarity you need, and go at it. Gas welding....as in oxy/acetelyne welding.....I know very few people who still do this, and I dont even know if they teach it anymore. But, some people swear by it. I know very little about it, so I can't really comment on it. The critical things to look at when buying welders...duty cycle (IMO 40% is bare minimum, 60% is better), this tells you how long the welder will run w/o having to stop and cool down. A 10% duty cycle means that it will weld for 1 out of every 10 minutes. 60% will run for 6 out of every 10 minutes. It is difficult for a fabricator to exceed 60%, unless you have a whole bunch of pre-cut pieces that are all set up in a jig. I usually find myself laying down a small bead (~10 seconds), stopping, moving to another location (to avoid warping the parts), which takes me 10 - 15 seconds, then another small bead....and so on. I have never exceeded the 60% on my miller. Next, look at output amps. Assuming you are getting ~28 - 30 volts, it is going to take 200 amps to weld 3/8" steel in a single pass, 250 amps for 1/2" (those are approximate numbers that will vary depending on wire speed, gas type, bevels on the working edge, etc., but are good for sizing the equipment you need to purchase). With a MIG, be sure to get something with steel drive rollers. And no matter which type you go with, get the 230v machine.
As for cutting, your gonna hate me for this....but don't waste your time with a torch. The price of plazma cutters is coming down, you can get set up to cut 1/2" plate for under $1100. The kerf is small and strait compared to oxy/acetelyne, the heat affected zone (HAZ) is generally very small (1/16" compared to 3/8 - 1/2") which equates to less grinding and less mess, and they are very simple to use. If you ever need to get into a tight spot, or cut something that you don't want to anneal (such as motor mounts, suspension mounting brackets, etc), the plazma cutter is the only way to go. The downside is that consumables are expensive ($35 per set)....but to be honest, I am still using the original set on my hypertherm 380...they are about 2.5 years old.
By far the most important thing, IMO, is to learn the process before you buy equipment. It will likely save you alot of $$$. Take the class! I cannot say it enough. Even with my welding ability (I have no problem welding roll cages, suspension components, etc.), I wish I would have taken the class. I would have started out at the level it took me years to achieve...meaning that right now I would be that much better. So take the class.
Take the class.
Take the class.
Take the class.
Take the class.
Take the class.
Take the class.
Take the class!!!!!
Seriously....take the class!
