I purchased a property tax lien for a premium. It was redeemed and I have a loss for the premium I paid and a gain for the interest. How should these be reported?

I purchased a property tax lien at auction.  I paid a premium for it.  The debtor has the right to pay the debt in full at any time.  (S)he does not have to repay my premium.  When redeemed, it seems I should have an expense for the premium and income for the interest received.  IRS instructions for this seem arbitrary and confusing.  I think I can: report this as a sole proprietorship where the premium is an expense and the interest is income (problem is that I get charged self employment taxes on any profits); OR report each lien separately with the interest being regular income and the lost premium being taxed as a capital loss (at a lower tax rate than the interest); OR elect to amortize the premium over some period and have that reduce the interest.  Can I do this last with liens for which the holding period is variable at the debtor's option?  If I can do this, what period should I be using for the amortization?  Finally, how would this get reported in Turbo-Tax?    Thanks!