I'm going to add some personal advice here. Not fact, just some personal opinions.
If I were you, I'd consider ditching the idea of learning the Z80 or 8088 (the latter of which is a horrible processor in my opinion anyway) and instead decide to use a modern Microcontroller as your starting point instead. This way you'll avoid the hassle of having to take care of all the RAM, ROM and I/O because it's already on chip.
I started my Microprocessor experience on the 6502, and although I learned a lot from building up a few projects around the 6502, and having to add my own RAM/ROM and I/O chips, it's experience which I've never actually used when doing my own modern projects. When I decide to use a Micro in one of my projects, I'd never consider using a bare CPU and then having to add all of the RAM/ROM and I/O seperately. I'd ALWAYS without exception use a Microcontroller.
The other reason I think you'd be better off starting with Microcontrollers, is that you'd gain much more employer recognition from it. If you were to put on your CV that you've experience with the Z80 CPU, your prospective employer would probably think....
"ok good, he understands Microprocessors. But we're never likely to use a Z80."
If, on the other hand, you could put experience with a modern Microcontroller on your CV, the employer would be much more likely to see your experience as actually useful.
I can recommend the PIC Microcontroller, mainly for no other reason than it's what I tend to use (other people may say the AVR or other Micros are better). Also the PIC has a HUGE resource of help available on the internet, as well as Microchips own website which details a massive range of application notes.
Oh, and MPLAB - the development environment - is free. And there are loads of free C compilers as well.
Brian