I'll try to answer some of your questions.
Yes, the computer, also known as the card cage, is located on the magnetics panel inside the electrical box.
The floppy drive is under the trap door on the side of the electrical box, seen in your photo #3.
There is a socket for an AT style (large round DIN style) keyboard plug on the Keypad Encoder Board mounted to the backside of the alpha-numeric keypads on the front panel. Some machines had an extension cable that mounted the socket on the outside of the Front Panel box.
The parameters are stored in a machine-language file called PFILE.DAT which is located in the B:\RAM directory. I don't think you can edit the file without messing it up and making it un-readable.
If the spindle is inverted, you should be able to run the machine on single phase 240vac. Just put the 2 hot legs on terminals 1 and 3 on the disconnect switch and make sure you have a good ground. There is a step-down transformer that creates the 120vac for the computer, monitor, and some relays and solenoid valves.
The Milltronics Centurion control has a very powerful conversational programming feature, but it also has a text editor built-in and will run Fanuc 10 style G&M code programs as well. I think $150 is a little steep for the manual, it is more of a reference book than a operators manual. Spend some time playing with the screens and ask questions on this forum, there is a wealth of knowledge available here.
That looks like a nice, clean machine, good luck with it.