Xserve Raid Windows Expansion Questions

1) How long will expanding the Raid take? Ball park? Say 10H? The Raids are full. Are the Raids accessible but slow during this period?

If they are RAID 5 arrays, this will take hours - about the same time as it would take to create the arrays in the first place.
Beware, though - the expansion process does not MERGE the arrays - the data on the expansion drives will be lost. Therefore is you add drives BBB to array AAA the data on BBB will be lost.
The good news is that the array will be available during the expansion.

2) What is the point of the Hot Spare? I dont really see any advantages to it vs a cold spare? It doesnt even save me a trip in to the office cause I cant assign it to the raid on the fly anyway.

The advantage of the hot spare is that if a drive fails the XServe RAID starts the rebuild automatically using the hot spare. If there's no hot spare then the rebuild doesn't start until you get to the office and replace the drive manually, potentially adding hours or days to the time you're running without a spare. If a second drive fails before the raid is rebuilt on the spare, you lose all the data so the less time you're sitting in a degraded state, the better.

3) After I expand the array with the spare do I have to merge it? I have read conflicting posts.

I don't understand the question given that you don't merge arrays.

4) Is it correct that I will have to use a Partition tool to get the OS to see the expanded Raid size?

Probably. That depends on the OS/partition format. I've never used an XServe RAID in a Windows environment so I don't know how Windows deals with the volume expansion.