1. Storage is important for big files. However for things like iTunes (with it's huge video files) just get an external to host the iTunes Library on. Plus REALLY consider getting a backup drive and use Time Machine or a cloning program. Just remember is not if a hard drive will go, it's when it will go.
Plus when I put an SSD into My older Mac Book Pro is became a different Mac. The boot time and launch times seem to put my Mac Pro to shame.
2. OS X loves RAM. However on my Mac Pro anything over 12G of RAM and it really becomes dismissing return. However if you are not crunching video then 6 - 8 G is a really sweet spot. Just buy larger and larger RAM along the next few months to spread the cost out.
3. Processor is kind-of important. In todays world cores and programs that can take advantage of multiple cores can really speed things up. Don't take my word for it, bookmark the Mac speed testing site BareFeets.com and Accelerate Your Macintosh.com.
Plus do some software maintenance about once every three months using programs like Yasu or Onyx or Maintenance and run all the cleaning routines. Let the program clear all the caches and let it reboot your Mac. Then upon that reboot manually reboot your Mac again to completely rebuild your OS X system startup/shutdown cache. Doing this about once every 3-4 months will keep your OS X humming along almost like new.
Mac Pro Dual 2.8 Quad (2nd gen), 14G Ram, Two DVD-RW Drives, OS X 10.8.3
2006 Mac Book Pro 2.16 (first Gen) OS X 10.7.4
2TB Time Capsule, 2 TB
32G iPhone 4S Black, iPad (3rd Gen) 32G Black