2. detach the 250 gig drive temporarily. Attatch the SSD and install the OS to it. After installation is complete, attach the 250 gig drive and change the boot order in bios so that the SSD is first.
4. Most apps allow you to choose where to save at. If not, you won't be able to download once the drive is full.
5. You will need to reinstall all your apps on the SSD or boot from the hard drive and use it.
You will essentially have two independent copies of the OS. Programs installed on one will not work on the other unless it is installed on it also. You can switch between OS's by changing the boot order in the bios.