Although the rent you pay will be based on the market rent of the home, it will be discounted by 10% from the market - and will be further reduced to reflect your investment in the house. For example, if you have a 10% investment in the property, you will be have to pay roughly 81% of the market rent.
If you staircase up by purchasing loan parts on the OnStep secondary market, you will receive the rent back for the loans you hold. This will in effect reduce the monthly rent you pay. This will happen from the day you staircase up.
The rent will be fixed for the first two years and then adjusted at the rate of inflation annually thereafter. For example if your starting rent is £1500 per month, inflation rate is 2% and you do not staircase up; your rent for year 3 of your residence will be £1530 and your rent for year 4 will be £1560.60.