Paul
Exceeding the £16,00o limit will result in your payments being stopped until you are back under the limit, you remain entitled to ESA subject to any reassessment of your claim.
If you are not entitled to payment then this includes any SDP that you receive.
There are no hard and fast rules as to what a claimant can spend their money on in this situation, it is entirely at the discretion of a Decision Maker whether any particular expenditure is acceptable or not. However as a basic rule, payments that reduce or pay off a loan or similar early are usually not acceptable.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems