1. Your Income & Expenditure figures on your bankruptcy form were presumably based on just benefit income. As such, it is likely that your expenditure figures were very low (because your income was also very low).
2. If you start work your income will increase and you MUST notify the OR within 21 days. However, your expenditure will also increase - partly because of expenses connected with the job (travel, possibly working clothes etc) & partly because your expenditure while unemployed will have been below what is normally accepted as reasonable. So, when you notify the OR of the income increase you must also notify the increases in your expenditure. It could be worthwhile getting some advice on this from a body such as your local CAB or by ringing CCCS before you finalise the figures.
3. Whatever figures you provide, the OR will assess them & may query them. If the figures he/she then accepts show a surplus of income over expenditure of less than £100 per month you will not have to make any payments to your creditors (unless your income increases again before you are discharged). If the surplus is more than £100 p mth then a % is taken - starting at 50% for a surplus just above £100 & gradually increasing if the surplus is larger. You will be asked to enter an Income Payments Agreement (IPA) to pay this amount, & the liability runs for 3 years. The amount can vary if your circumstances change, & you have to notify any changes throughout the 3 years.
4. Any IPA will not delay your discharge, which will be after 12 months (unless there is any other reason to delay it), but discharge will not end the liability to notify as stated in 3 above.