Gotta say it's worth listening to Jazz. I think what he's partly going on here is that judging by your answers you have a very steep learning curve to get up and also it's not really clear what sort of machining knowledge you have 'in the bank'.

Do you already have a metalworking business and/or workshop? It's just concerning that you don't know e.g. that machine vibration comes from cutting...

Point is, your ambition is admirable but what you're intending to do is to a major project for an experienced, very well equipped machinist who is already up that learning curve. To 'properly' design such a machine to the extent that it will be good enough for commercial use requires degree level understanding of mechanical engineering and manufacturing and measuring facilities which cost serious money.

It's the size of project you might tackle when you're confident of your skills. Not as the first project: it's so big that everything about it, especially any mistakes, will be expensive.

Follow the link I posted to the Milltronics machine and read the PDF brochure and specification there to get an idea of what a commercial machine can do. Bear in mind that this sort of machine will cost as much as a small house... and has many million pounds/dollars of design and manufacturing capability behind it in the company that made it.

Re machining level surfaces 'at home'. What reference would you use to check things are straight and level? What instruments would you use to determine how far off straight and level they are when done?

My suggestion is this: start by making a 1/10th scale model of the machine you intend to build. Or even smaller: make the longest axis shorter than the longest travel on your largest current manual milling machine (you do have one?). This'll make life a whole lot easier.

You'll probably be able to build the whole thing for less than the cost of steel for the monster machine and you'll learn a hell of a lot. A small machine can still make money for you (e.g. engraving nameplates etc) but you won't be spending major sums on something that may not deliver. Go for a stepper not a servo system (so just a few hundred dollars) and just get the damn thing working. Then you'll have a better start point to build the monster machine if you still want to try.

Sorry to be less optimistic this time but there's no shortcuts: if it was easy to build a huge machine like that and start the money rolling in, a lot of people would have done it. Jazz is right to give a bit of a reality check.