Hello!
I would keep the oracle binaries on the root disk but its just a matter of taste! Do as you like. If you have 36 gb root disks it seems like a waste of space to me to just use them for the OS.
I would recommend setting up the raid before installing oracle. There is always the possibility of doing something wrong and wecking the disk config considering you are pretty new to the Solaris disksuite. (you will understand once you give it a try! Keep focused!
)
Yes you can make on big stripe of all the disks but consider the fact that if one disk breaks the volume will break! So i would recommend making a mirror of the 2 internal disks and then 2stripes with 3disk in each and then mirror them.( that will give you 3x36gb of space to play with) if you are gonna use it in a production environment. If its just for a test do as you want.
What i recommend:
Mirror (raid 1) of internal disks
/ 7gb
/var 3gb
swap 1gb
/orabin 20gb
raid 1+0 of 6x36gb diskpack
/oradata 108 gb
Disksuite works with slices so you can have like c0t1d0s2 c0t2d0s2 and c0t3d0s3 as one disk and use c0t1d0s0 for something else.. (Read the docs on sunsolve)
Cheers
/peter