All the countermeasures you have mentioned will not really save you any energy during the cold season. Wrapping the line set might save you a hundred watts or less, the shorter the lines, the less potential gain. Actively heating your outdoor unit is probably already being done by a crankcase heater in the compressor.
Trying to force longer operation or less defrosting by adding heat is the wrong approach. Besides the fact that the supplemental heat transfer operation is inefficient, the heat pump is at its worst performance. Your gas backup furnace is most likely less expensive and much more effective to run. It's up to you: run your heat pump to death at half its rated heat output or let the furnace put out 500 percent more heat on a duty cycle. As temperature plummets, the furnace may become 10 times more effective compared to the heat pump. Depends on lots of factors.
A better approach to get the most out of the heat pump at low-temp operating conditions is to check out, and improve if necessary (or possible), the defrost cycle. Many of the earlier units and some of the nit so old units just defrost for a set period whenever the outdoor coil is below a certain temperature. How much frost and how long it takes to melt is irrelevant, the unit has a set defrost time. Newer defrost controls use ambient sensors, defrost termination sensors, and algorithms that save lots of energy. Not only does the unit spend less time sucking heat out of your house to defrost, some defrosting operations are skipped entirely by lack of demand.
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