logic 8 questions

I bought a mac not too long ago because of the ease of creative expression that typically goes along with mac software. I bought the Logic 8 studio sweet, and a terabyte of storage so I could have AMPLE space for my music projects.

I am in no way proficient in ... the workings of the mac os.

My questions (and I am SO grateful for help here)

I want to be able to save stuff on my external drive without it taking up space on my computers hard drive. The same goes for my iMovie - which I use to post videos on youtube.

In any event, projects in either of these programs tend to be quite large. A terabyte is much more... withstanding to this kind of storage and use, and I have a really nice one with good drives, so it would be much better if I was accessing my files from that. I can't really find a way to make my files save to the external drive by default, and dragging/dropping them into it still leaves files on my hard drive. I am hesitant to delete them because of stuff like permissions? Is this something I should be worried about? Also, the other thing I did was drag and drop Logic and ALL of my plugins and stuff into the hard drive - it asked me to authenticate by entering my password - does this mean that my software and plugins are safely on the drive and can be accessed should my computer take a sh*t and die?

I KNOW how long winded that is - it really boils down to one thing - I want to know that my software and files are backed up on my external drive so that I can delete the files from my MacbookPro's hard drive and save myself space so that everything runs faster and stuff (aside from the software that I actually have to run). I DO have time machine ... if there's a forum I can go into so that I can learn about setting THAT up a little more efficiently, I'd appreciate it SO much.

THANK YOU! I appreciate the time you even take to read that.