the 8088 is a variant of the 8086, but with an 8bit external bus, instead of the 16 bit ext bus found on the 8086s, and a smaller prefetch queue. It'll work, but depending on the instruction order, you may see some performance loss with the 8088. The Execution units are identical between the two, though.
*EDIT*
And why CGA? You can use EGA and CGA mode on the 8086 with a compatible EGA monitor and EGA card. I used to, when I got my first 8086. Half the games I was given at the time used CGA, whlie others used EGA.
*EDIT 2*
As far as speed issues, you can use utilities like MoSlo (if it's still around) or others, that'll throttle the machine down to real mode x86 speeds.
*EDIT 3*
The NEC V30 is a pin compatible reverse engineered 8088/8086 compliant part that also supports the 80186 instruction set. Even IBM used them in certain PS/2 models, so I don't forsee any compatability issues. That said, I've never used a V30, so take that with a grain of salt.