Please help - new to Mac. Storage options for 11" MBA 128GB

Hi,

I am a PC laptop user considering moving over to a MBA 11". I need portability and I'm worried about the storage capacity for the MBA at 11" - I'm on a budget. The next step up for me would be the 13" MBP for storage space/cost (and then I start getting confused about Serial ATA/SSD).

I currently estimate to have about 80-90GB of files on my PC (I estimated this from what's on my PC, and guessing at extras on my external HD). Most of this is music and photos from years of travel that I do not want to lose. My external HD once stopped working and I lost photos, so I never want that to happen again.

I understand I can also get an external HD for the MBA, as well as back everything up with Time Capsule/Machine.

Are there any other solid options?

Is it too risky to store all music/photos solely on external drives, leaving the main machine free for work?

The main things I will be using it for are writing, iTunes, streaming TV/movies, web browsing and blogging, and some light photo editing.

Thanks for your help!