Up-to-date employment letter question

[pooky]

Hello everyone,

I'm planning to apply for CEC soon.
I have two questions regarding the up to date reference letter from employers:

1). When should I ask for letter of reference from my current employer whom I started work for since June 2011.
2). I didn't end well with my previous employer, so they won't give me the letter so how should I write an explanation for that? I do have the T4 and monthly pay stub from a government calculator. What letter of reference should I make up?

Also, I do have bits and pieces self-employed work during last 3 years prior to my intended application, how should I do about that? Would that affect CEC application?

Thanks everyone for helping!