A few additional comments
1) There is no way an engine with two dead cylinders would make minimum static RPM although it would certainly make runup RPM. There may not necessarily be a lot of vibration depending on which combination of cylinders are dead, thus the importance of a power check a the start of the takeoff roll
2) While a quick check of the engine instruments to ensure they are in sensible possitions, is a very good idea at the start of the takeoff run the mantra "in the green" is often mindlessly applied to all flight regimes. This is a particular pet peeve of mind. When established in the cruise the engine guages should be checked regularly but not to assure that they are "in the green", rather to note the exact position of the needle on each guage and then ask the question " has there been any substantial change". If the answer is yes, then some thinking should be given as to why. Engines almost never just up and stop, they will almost always give some warning. For example impending catastrophic internal failures are almost always preceded by rising oil temperatures and declining oil pressures. By the time both have exceeded their red lines you had best have a field ready for the forced approach. If you have being paying attention you would have seen the situation devloping and started a diversion right away with the likely result of a uneventfull landing at the nearest airport.
2) Re the question of descent and leaning. This is what I do (for your typical trainer/light tourer with a fixed pitch prop and no multi probe EGT guage)
a) Slightly enrichen the mixture
b) Establish a nose down attitude which will give a 500 FPM descent rate
c) As the aircraft accelerates the RPM will start to rise so,
d) Reduce the throttle to maintain the cruise RPM I had before the descent
e) Trim
f) When I reach the desired attitude fine tune the RPM and relean
Prior to starting a descent, one of the worst things you can do is go to full rich, particularly on cold days and for long descents as this dumps a load of excess fuel into the cylinders which will cause the cylinder head temperature to dramarically drop, a great way to cause cylinder head cracking.