GB struggling with power issues- What do I do to make it work?

I have an imac Lion 10.7.4 with 4 GB 1333 MHz DDR3.

Ive recorded a whole album over 7 months and I am aware if you use too many FX etc you are putting strain on GB to perform properly.

This is what Ive done to make my Imac work as well as it can ..what am I missing please.

1 Lock tracks Im not using whilst recording others

2 Moved all songs into an external hard drive apart from the one Im working on to free up space on Imac etc..

3.Use fx sparingly (ususally only echo and reverb and visual eq are used in mastering a song ) I use Alchemy and get all the FX etc set up on there for each sound so as not to use GB's strained power on its FX system.

4.Each song uses minimal tracks.....7 or 8 tracks for each song..they are not complex pieces and are only 3 or 4 minute pop songs.

Is Optimizing the answer and how do I do this. Will it make all the difference??

I am no tech head...do i need to install more Ram in the back of my Imac to make it run faster or is GB just not very good at running on a standard Imac??

P.s- why why why am I getting random crackling in GB all of a sudden ...is this related?

I would really appreciate some advice from anyone that knows

Thanks

Paul