You can use much more modern SCSI drives on an SE. I have a 9.1GB in my SE, a 36GB in my SE/30, and a 75GB in my Quadra 950, there is no drive capacity limit in their hardware. Narrow SCSI is narrow SCSI, many, though not all, modern ultrawide SCSI drives will clock down and work just fine with cheap
$15 pin-adapters.
There is a 2GB partition limit under system 6 and early system 7 releases (you can have as many 2gb parts as you want though), I can't remember for sure but I think it was somewhere around 7.5.3 that you could have up to 2TB partitions, though that's impractical with some other file system limitations like maximum number of files and huge block sizes.