Burning files across multiple CDs or DVDs

Not sure if OS X's built in Burn can do it, but Toast Titanium can span disks.

Yes. If the data you choose to burn will take up more than one disk, spanning is automatically chosen and the interface tells you how many disks you'll need. You have the option to "Avoid splitting files when spanning". A good precautionary option if you're worried about an important file not reading back off a disk it has to cross over to. You end up with as many normal disks as it takes. There's no need to read them back in any particular order as long as you don't let it split files.