Pls help - salaried + self-employed merged Earning

[sorabzone]

HI Experts,

I want to apply under Tier 1 General Highly Skilled worker category.
I am in India and need to show £40,000(after multiplying my earnings with uplift ratio).
My annual income from my full time job is not enough for this.

But alongside my job i am also maintaing computer systems & network setups for some small business firms(all registered).
I got paid by cheque from these firms and i can also get some declaration on letter head or other document if required to verify the genuineness of my earnings.

Query 1 - Can i combine my job salary along with the income i get from other sources .
Query 2 - what documents i need for this.

Thanks in Advance

Saurabh