Hard Drive Configuration for my setup
If there is room for more drives, order more drives. If there isn't room for more drives, order more drives... and an external enclosure.

I'm assuming this data has at least some value to the business and from your comment we can also infer that you're experiencing performance issues already. So, zero redundancy and single spindle performance isn't going to cut it.

If you absolutely have no other choice than to stick with these 5 drives, I'd probably go for a 4 disk RAID10 with a hot spare. Possibly, maybe, all 5 in RAID5. Separating tempdb and indexes at this sort of scale is pointless.