I've read some threads and noticed that it's in my best interest to do the Time Machine config before other configs. Some questions:

1) I have another 1 TB drive to install. Should I do that first?
2) After I set up the Time Machine share for a specific size, can I change that later on? I have about 4 Macs that will do Time Machine Backups and I've had one 120GB Macbook create a 500GB TM backup before, because I needed the detailed history on it. I know that my TM share will end up pretty large, hence my purchase of this.

on 2) yes, you will be able to resize (since v.2.5) the backup disk image without data loss (verified!!!) - ignore official manual that misinforms about data loss during resize. You just need to stop (unmount) backup disk, enter new size, select Resize from the Gear menu.

Pay attention, that the new size should not be more than available free space on that HDD where the original backup is located (one file can't cross the HDD) and should not be less than your data on it. Actually, you will be notified if some of this cases happen (at least I was).

Also, it would be better to de-fragment your HDD right before resizing, otherwise you might get "contiguous space" problem.

Thanks. Hmm, sounds like I'm better off adding the new HDD before attempting the TM.