Mac Mini :: Internal HD Full - Wanted To Upgrade To 8GB?

I'm a newbie desperately seeking tech advice on how to remedy a full-to-overflowing 160GB internal HD problem and add more RAM. I have a 2009 Mini (2.26 core 2 duo, 2gb 1067 DDR3 RAM), along with a pair of 1TB external USB HDDs (one 1TB external USB drive dedicated for time machine), and a 3.5" 300GB Velociraptor drive borrowed from a friend. MOst important to me is I want to absolutely minimize any chance of jeopardizing/risking losing ANY files/data already on the drive or avoid any time-comsuming selective file deletion just to make room on the "Macintosh HD" internal drive.

One friend suggested I make a bootable clone of my internal drive onto a larger drive, which I did with a program called SuperDuper, i made the copy onto the Velociraptor drive. Presently the WD raptor is running on an external USB docking station. Then I was told to make the external drive my startup drive. However, all my external drives use USB (no Fire wire interfaces). The problem is when I go to system preferences the only startup disk choices are the (full) Macintosh 160GB HD and Network Startup. I cant for the life of me figure out how to specify one of the external drives as a startup disk, although the 3rd party application SuperDuper! claimed to make a totally bootable clone onto the Raptor drive.

As a short term solution, I also received advice on copying a bunch of the larger files, like my iTunes video library (at least 50GB) onto one of the external USB drives, deleting the contents of the Movies folder on Mac HD, and inserting an alias for the files or folder pointing to the copied movie files destinations on one of the external 1TB USB disks. I'm scared it will adversely affect iTunes being able to find the files on the external drives. Can I make an alias for the whole iTunes Movies folder or do I have to make them for each of the files I copy?

I need to summon the courage to try and open the Mini case and see if I can implant the cloned drive ultimately, but I wanted to try and get it to boot externally first before I got into the innards. Anybody have a link to a photo or video step by step how to on the actual case cracking operation?

explicit how-to directions and advice on how to fix these issues and/or assist me with several links on how-tos that I can use in terms a simpleton like myself can implement without risk of losing my precious files.

Expressed another way, what I want to do is simply upgrade the internal drive with a larger and faster drive without any risk of losing data. I was thinking there out to be a relatively painless route to employ an external drive to function as a logical extension of the internal drive, so that OSX would see the stock internal drive plus an external drive as a single "virtual" volume. Although pricey, I was considering a SSD drive for significant performance increases.

As to RAM upgrades, what type of memory slot arrangement is inside the case? I wanted to upgrade to 8GB, but 4GB would be acceptable. I need some recommendations on what type of RAM modules to obtain to make this happen.

Most of all, I am seeking knowledge and experience from expert users to learn from. Tremendous thanks in advance for anyone/everyone who can help me and teach me.

I look forward to any kind and generous folks willing to help me learn.