For such amount I need at least 35ETH, intersest at least 7% and prefer keep collateral by myself, you should agree with my terms:

In the event that the value of the collateral falls below 110% of the principle then I would have the right (but not obligation) to sell the collateral at the best available price, as quickly as possible. (After gives a chance add additional collateral).
In the case that I am not able to sell the collateral for an amount enough to cover the principle plus interest then you  would owe me the difference.