In Ohio, I know you cannot foreclose until at least 1 year after the Tax Lien Certificate is sold at auction. It cannot be resold to the owner of the property. As for your other questions, I don't think you can mark them up, but I'm not sure so consult an Ohio Real Estate Attorney.
Steve Baldwin liens may not be the best to mark up as they are resold for pennies on the dollar. A lien only makes sense if it's performing and priced less than 20% I think. Maybe chat with one of the tax lien guys. I do know that the less it's performing the lower the price.
If you do decide to sell some let me know :-)