If it is a Z80, then 8 of them are data lines (for external memory) 16 of them are address lines (for external memory) and the rest are things like /RD and /WR, Halt, external interrupts etc.
You will also need an external clock, i.e. you can't just hang a crystal or a resonator on a Z80.
If you get as far as connecting up your external clock, external EPROM, external RAM and external I/O, you'll still only have a Z80, which will draw a lot of current, and, IMSNHO, is one of the clumsiest and badly designed processors of all time.
Also one of the first to attempt the "faster clock = faster programs" confidence trick.
Some of the operations involving IX and IY index registers took so long, that a colleague of mine theorized that the registers didn't really exist, and that the CPU was actually saving the swapping the HL pair with the notional index register, permorming the operation, and then swapping back.
Having said that, I know that I was spoilt by experiencing the 6809. Possibly the best 8 bit processor of all time.
Some people swear by Z80's, I tend to swear at them.
My advice is to throw the evil things away and get yourself a cheap AVR or PIC to learn on. Or maybe an old Babbage difference engine.