most standard CDs hold standard amounts of data up to around 703 MB that can be read in almost any CD-ROM drive, the physical/actual amount a CD can hold is actually around 1207 MB, some drives can read these, some cannot, overburning is when you burn more than 703 MB of data to a standard CD-R
depends on the drive, usually its no problem at all
other common formats are .bin/.cue for VCD's and SVCD's which can be just over 800mb
you have to understand that the actual disk itself even if labeled 700mb/80min is based on the iso9660 filesystem which like any filesystem takes up space all by itself, by using a different filesystem with a different node setup and size you can squeeze alot more on there provided the drive will read and write to it that way
If the file-system is just bits (which it must be right?), then what does it matter what is being burned as long as long as whatever app is controlling the burn can send those bits to the writer? Reading it is another matter, but shouldn't any drive be physically able to write any filesystem?