Nope, you can use partitions larger than 1GB, but the system will report odd/impossible figures for the size because of the signed addressing that the FFS uses. Most of the time this matters not a jot, but occasionaly it will send somthing haywire, so it's safer to avoid the possibility.
If you're only using 500MB the you could have 3x ~8O0MB in the rest of the drive with no prob's, or 2x 1GB and a 400MB.
To be honest their are no right answers for the partition siszes, just what is convenient and reasonably safe. If you want you could set the drive up with lots and lots of partitions of 1MB (unformated) to replicate floppy disks - but each partition uses some memory, so this is probably a bad idea
equally, just having one BIG partition will slow down access and any disk operations (optimising, de-frag etc) will take a very long time. I settled on the sizes I recomend coz they work for me.