Tier 2 General Supplementary Employment Procedure

Hi,

Can you please help me in finding out the correct procedure for supplementary employment of a Tier 2 General Visa holder.
I have a Tier 2 general Visa and I am eligible for a Supplementary work of 20 hours / week with an employer other than the main employer who is my sponsor in CoS.
* Does the supplementary employer needs to sign up an employment contract with me for the work (which should not exceed more than 20 hours / week and the work will be done outside office hours) and pay me salary through PAYE (deducting tax and NI) ?
* Can the Supplementary employer pay me on hourly basis as the work should not exceed 20 hours a week ?
* Is there any limit for the salary paid by my supplementary employer ?