About the format used for installing wii backup games
it really depends on what game launcher you decide to use. for usb hard drives you can't go wrong with "USB Loader GX 3.0" or NeoGamma. I like USB Launcher GX, it has a nice gui(graphical user interface) and just a finished feel to it, and if you like them there are tons of skins, though i think the original ui looks best. Both support WBFS formatted, and i think usb launcher supports fat32. I have yet to hear of a launcher that does not support WBFS formatted drives.
In the end you really can't go wrong by choosing fat32 or wbfs just as long as your launcher supports the choice, one thing to keep in mind is that you will need a different program to read your wbfs drive (try Wiii Backup Manager) , your computer will tell you you need to format the drive before you can read it because they usually don't recognize wbfs Do not format it, just manage your backups with a wii backup managing software.
As for splitting the drives into different partitions, I have no idea if you need to do that (i feel like you will only need to do this if your disk is very large in size like 16gb vs 350gb vs 1tb) , i do know that i used a 16 gb micro sdhc card with a usb adapter to store backups for a while it was formatted to wbfs, and i did not partition it into pieces it worked. that but you might want to partition it just so one partition can be read by your computer and used to store personal data like movies and music. Use a program called "EaseUS Partition Master 9.1.1 Home Edition" it's simple and easy to use i created a 90gb partition for my 350gb "my passport" drive and a fat32 partition because some disk rippers for the wii (like clean rip only reads ntsf and fat32) wont use wbfs and, i can then rip the disk and view the files within the stock windows explorer. make sure if you do partition your disk to set the wbfs it to primary instead of logical and make the partition active do the same to any partitions you want your computer and launchers to be able to recognize in explorer. USB launcher can recognize logical drives and primary, some launchers only recognize primary and your computer will probably need a different program to view the partition instead of in explorer.
I prefer game installing using usb launcher, no computer is needed to backup your games to a hdd. just click install, and wait about 10 minutes and its done.
-Fat32, NTSF, & WBFS can all be used in wii game launchers,
-with a wbfs partition you will not be able to view backup files or place them onto the partition without the use of a wbfs managing program
-fat32 and ntsf are not supported on all launchers, wbfs is on most, well atleast i haven't seen one that didn't support wbfs
-USB loader GX 3.0 supports installation of games, wbfs, and i think fat 32. NeoGamma supports wbfs
some good game launchers:
neo gamma-i like it and would use it if needed, supports gamecube and wii games
cfg usb loader-i use it and prefer it, supports wii and gamecube games
usb loader gx
i apologize for the scattered order of my writing, sometimes i will get off topic and start a new one then continue it later. good luck for soft modding your wii i would recommend trying modmii