A few points:
The water cooler is a minimal power draw, and the welder draws much less than 50 amps, so that will not be an issue. With a one man shop you will probably only be running a few things at a time. 50 amps will run your welder, the lights and should even be ok with an average air compressor coming on. Something that would be impossible with transformer welders. (a 250 amp Miller Syncrowave draws 98 amps plus, while a 205EX is only about 35 amps)
Using the tap water cooling method works very well. I worked at a shop that used that for over 10 years on the same torch with no issues. The actual amount of water used is pretty small, so we just drained it out a hole in the wall and let it puddle in the parking lot. Even after a full day of welding the puddle wasn't an issue. And the water quality wasn't great. A torch mostly has brass and copper wetted components, so unless you have acidic well water, no problem. The corrosion will be comparable to copper pipe, lifespan wise.
You can split up some of your electrical work, to lower the cost, and since you are not totally sure of what your needs are. However, try and pick components that will allow for the most flexibility and future expansion. Like the difference between a panel with 4 breaker spaces and one with 10 is only about $20 and the labor to install either is the same. But it will drastically change the cost of adding more things down the line.
With a welder, a lathe and a mill/drill there isn't much you can't do. Either recondition, or just make a new part from scratch.
Long arc, short arc, heliarc and in-the-dark!