There are many, many different ways to approach this question. It highly depends on what kind of work you intend to go after.
Sanitary tubing and pipefitting takes a very different machine than production aluminum fuel cells which is different than heavy steel fab, etc.
I own a small welding and fab shop. I can give you my experiences, but they may be (probably will be) different than yours. My shop is a job shop, and we do a pretty good mix of just about everything.
I started my business with a Miller Dynasty 200DX and a Lincoln Invertec V300 - PRO with an LN-7 wire feeder.
I bought the Lincoln first to do mostly MIG work, but I did do stick and scratch start TIG with it until I got the Dynasty. I bought the Dynasty about 6 months after I got the Lincoln.
The Dynasty is AC/DC and portable, so I could do light aluminum, portable welding, and delicate tig work. It also is a dynamite stick welder.
The Lincoln was a great wire welder for heavy work. I didn't use it as often, but I was glad I had it when I needed to run some dual shield or big wire.
I would recommend getting something resembling that combination to start. A small-ish (200 amp or so) AC/DC TIG machine and a 300+ amp good quality wire welder.
Brand isn't as critical as local support. Get whatever brand your local welding supply sells and services. These guys will be a CRITICAL vendor, so make sure you keep a good relationship with them.
All in one machines are fine if you have others as backups, or if you have a MAJOR space constraint. But if your one machine shits the bed, you're dead in the water until you get it fixed. When you're a hobby shop, this isn't a huge deal, but when you're earning your living with a welder, you can't afford to not have it working properly. If for no other reason, this is a good reason to have two machines.
Once you start hiring employees, you will want multiple machines anyway. I am now up to 7 welders for 3 guys, with plans to buy more. Diversity and the ability to specialize machines is very useful.
As far as buying cheap vs buying nice, I would strongly advocate buying the best you can afford without putting yourself in a bad spot financially. If this is going to be a money making venture, you want quality equipment that you can count on to do the job.
Cheap tools work fine for a lot of things, but I don't like relying on them for my living. It also ***** having to buy things twice. I'd rather just buy the one I really want than buy the cheap one and eventually have to buy the nice one later when the cheap one dies. If you end up needing to get rid of a machine, good quality brand names hold their value a lot better and you can recoup a lot of your investment if you take care of it.
I can't really recommend brands and models for you, I am not intimately familiar with European welding brands. I do know Fronius is an industry leader in cutting edge welding tech, and their machines are extremely nice. I also know Lincoln is a solid, reliable company. I personally have all Miller welders.
As to whether it is wise to start a welding business without any welding experience, well,
That may or may not work out in your favor. I probably wouldn't hang out your shingle until you can do work worthy of selling. If you can pass a few different bend tests and your welds look aesthetically pleasing, you're probably ready. If you don't know your *** from your elbow in welding, how do you expect to do what the customers want to their specs?
In my experience, at MINIMUM you will need to know how to read prints, interpret weld symbols, know how to select process, filler metals, gas, and base metals. You need a working knowledge of basic metallurgy, as well as some knowledge of the adjacent trades like machining, sheet metal, pipefitting, construction, ironwork and any other industries you might do work for.
Welding shops usually need some support equipment too. At the minimum, I would want an oxy-acetylene torch, grinders, cut-off saw, air compressor, plasma cutter, drill press and a welding table. You're probably going to want a computer with some kind of CAD software at some point too.
There is a lot more to this business than just welding parts.
