Chipsets indeed prove a challenge, but it’s not insurmountable. QEMU’s emulation of a G3 tower is a decent example of this.

There’s decent availability of PCI and AGP GPUs supported by OS 9 and early OS X, especially if you include PC variants that can be flashed to work with Mac OS, so I wouldn’t worry about video too much in the short term… just make sure the motherboard has a PCI or AGP slot.