Hardware HD choice...

Hello,

I have to choose a dedicated server to host a big 8.3 database.
The global size of the database (indexes included) will grow by 40 Go every
year (40 millions of lines/year)
Real data (indexes excluded) will be around 5-7 Go/year.
I need to store 4 years of activity.
Very few simultaneous users (~4).
100000 rows added every day via csv imports.
The application will be a reporting application.
Main statements: aggregation of 10000 to 10millions of line.
Vast majority will hit 300000 lines (90% of the connected users), few will
hit more than 10 millions (10% of the connected users, there may never be 2
simultaneous users of this category).
20sec - 30sec for such a statement is acceptable.

It's quite easy to choose CPU (xeon quad core 2.66, maybe dual xeon), RAM
(8-12Go) but I still hesitate for hard disks.

these are options possible with the hosters I usually work with:

Option 0)
RAID1 750Go SATA2

Option 1)
RAID1 750Go SATA2 + 500Go USB disk

Option 2)
RAID1 SAS 15000rpm 147 Go hard disk + 500Go USB

Option 2+)
RAID1 SATA2 SSD intel X25-M 80Go + 500Go USB

Option 3)
RAID5 SATA2 5x750Go

Option 4)
RAID10 SAS 15000rpm 4x146 Go

Option 5)
RAID10 SATA2 4x250 Go

Any other better option that I could ask for ?

What would be the best choice in case of an external USB drive : using it
for indexes or x_log ?

And what is the best option to backup such a database ?
Nightly dump ?
data folder zip ?

thanks for your help.