looking for external drive buy suggestions

[gosha]

I finally decided my self to spend some money on an external drive. I will use this for backups but I would like to keep it always on and use it simply as extra space to use any time.
Looking at the prices around, 1T seems to be the best deal, I'll be able to store all my stuff and have plenty of space for the future (at the moment I have less than 200g of files hanging around in three drives, one of which with a lot of bad sectors).

Specs always say that the drive's software will work with Windows n. I guess it will be recognized fine by OpenBSD, but will I miss anything interesting without that software? Are there any external drives designed for unix?
Is it fine to leave the drive always on? Will it be noisy? What about power consumption?
Also, I guess to have a 1T partition is not a good idea. I will not format the whole drive, just start to use the size I need. Any suggestions on partition size? What about sector size (I have one huge file of little less than 100G, yes hudred gigs, should I take any particular care in making a partition for it with special sector size?)?

Lots of question marks...