Twins on a SIB is going to wreck yer head - in so many ways.
My advice is buy a decent engine (not new perhaps, but a good example with some history) and keep it well serviced. Learn how to sort the basic problems that occur at sea and carry a decent spares/repairs kit. After that make sure you have a very good anchoring system and a VHF. Help is never far away.
Bear in mind that IF the wind and/or tide is going the way you want, a pair of oars will be very useful and never fail to start
Common engine problems are:
Water in fuel (easily guarded against)
No fuel - ditto
Damaged fuel line - carry spare
Broken starter rope - carry spare and tools
Oiled spark plugs - carry spares and tools
There is some useful chit chat about SIB equipment and spares here: Linky