I have flown both glass and steam. IMO once to go glass you will not want to go back. Glass has a lot of information that is not available on steam gauges. And once you get used to it you don't feel overloaded, you just absorb the information.
As for the backup instruments, they are required under current FAA regulations.
Another system is the EFD/MFD1000 system by Aspen Avionics. At 15000USD about half the cost of the G500H. You can add synthetic vision and moving map modules. It is setup to display with or without the information tapes along the sides. So you can use it to train both steam and glass.