web server config

[BizTalk]

Hello

I am a tech for a small organization and we are web server is running windows 2003 web server edition. The server has 6-9.1gb hard drives which is on software raid so what i did was setup a mirror drive for the drive that has the os on it and setup a raid 5 for the other drives.

The thing is i have 4 18.2 hard drives and i plan to replace the main hard drive and the mirror so when it's time to do this how should i go about doing it?

I also plan to replace 2 of the 9.1 hard drives that is in the raid with 2 of the 18.2 gig drives, will i run into any problems with this?

The last thing is i notice that there is 50% overhead on the mirror drives and 25% overhead on the raid 5 drives. Is bad?

How will that overhead affect server proformace?