> Do we emulate transferring x length of bytes to a buffer in another part of hardware (video ram for example) one system bus wide word at a time or do we just cope it all at once and move on? etc.

Syncing aspects of the emulated hardware with each other is easy. You still have to count clock cycles somewhere. So you just execute the necessary number of CPU cycles while your DMA is running, then set the flag that it's done or whatever. And you have to do the same thing with hardware timers anyway — you trigger an interrupt after X clock cycles.

It's syncing the emulator itself to real time that's tricky.