[CentOS] RAID Hot Spare

I've googled this question without a great deal of information.
Monday I'm rebuilding a Linux server at work. Instead of purchasing 3
drives for this system I purchased 4 with intent to create a hot spare.
Here is my usual setup which I'll do again but with a hot spare for each
partion.
Create /dev/md0 mount point /boot RAID1 3 drives with 1 hot spare
Create two more raid setups
/dev/md1 mount point /	RAID5 3 drives with 1 hot spare
/dev/md2 mount point /home  RAID5 3 drives with 1 hot spare
Now do I create partions of equal size for each set then if I remember
correctly when creation the RAID there is a check box for hot spare. Do
I just marry the 3 equal partions, click the check box and assume the
system will find the partition of equal size and use it when needed?
Makes no sense to me.
Of couse will be creating RAID0 swap but leaving that out of the
question for obvious reasons.