Actually, 4MB is quite a lot. I do work with computers and I added a tonne of documents with my LOE. I am a CEC applicant and although I was not required to add these documents, I still went ahead and added them so that the visa officer could corroborate my history with the documents:
1) LOE
2) My previous work related letters that I didn't add with the reference letters since I didn't claim points from them.
3) 6 months of my bank statements, T4's and NOA.
4) Education Documents that I didn't claim points for
5) Educational documents of my wife that she didn't claim points for
6) Work experience letters of my wife (she didn't claim points for them either)
In the LOE, I clearly mentioned to the visa officer that although these documents were not required, we still added them so that he could be satisfied that we are genuine candidates. I created a single PDF and added all of them into a single file and then through adobe acrobat, I compressed everything under 4 MB.
