Self employment documents for ILR

[dazzle]

Hello everyone,
Hoping for some advice please.
My wife will be applying for ILR at the end of this year and we want to plan in advance to make sure we get documentation right.
She applied for her first spouse visa in December 2009, and we have been living in the UK since December 2012, so she would be applying under the old rules.
We have been self employed in a partnership since July 2013 as an online retailer, making about £20k p.a. before tax. We are VAT registered, just in case this makes any difference. I am doing the accounts myself for the time being.
I am also in full-time employment, but my industry is quite unstable so there's no guarantee that I will be at the end of the year, which is why I want to cover all bases and have a backup plan with this self employment.
What kind of documentation should we be keeping to one side for the self employment? Is there anything else we can be doing now, which will make our lives easier when it comes to the ILR application?
Thanks in advance.