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I am not a professional so take my advice as it comes. My approach is to select a default of 20. The reason is two fold. First, the majority of general purpose kitchen knives recommend that angle, and second it is a good angle for general purpose use whilst not making it too fragile. I would have thought that 18 would also be a good compromise. When I do use a smaller angle I advise the owner to reserve that knife for fine work et al to prevent damaging the knife. All of my sharpening is for home use by non professionals so I rarely use a smaller angle.

There is the Tormek plastic matt but a much cheaper option is one of those silicone dog or cat trays from Amazon or your local pet supplies. Just get one with similar dimensions as the Tormek.

With the prevalence of diamond and CBN the sharpening difficulty is not so relevant anymore

The intro is not quite correct. There have been many refinements over the years which is patently obvious but otherwise quite interesting.

That can be a life saver (figuratively of course) for larger holes on lower power drill presses where the burr on the underside of the material can catch and stall the machine. 

Still, from a physics standpoint, in a situation where a solid moves in relationship to another, the friction coefficient is the ratio of the tangential force to the normal force. If there is no friction, there is no tangential force applied to the material being cut, so no work being done and obviously no matter being removed.

The work being done can be measured by the material being removed (bonds being broken within the steel) and the generation of heat. You need to maximise the first and minimise the second. We want as little heat as possible and as much material removal as possible for maximum efficiency. This is achieved by ensuring that the relative MOHs hardness of the abrasive is higher than the steel, the abrasive keeps as sharp as possible (friability helps with this) and the surfaces slide past one another as smoothly as possible, which is done by lubrication. The lubricant also assists in removing any heat that may be generated by friction. Water and oil have both been traditionally used on sharpening stones.

Eventually found that my trusted ceramic stones just couldn't handle the harder steels, loads of work, glazing on the stones,

There are different ceramic compounds and they have differing harnesses. It really depends on the MOHs hardness of the ceramic in the stone.

Friction is nothing more than generating heat.

Indeed, the water actually acts as a lubricant as states by Tormek.

The bond strength is not the issue. The critical factor is the MOHs hardness of the abrasive compared to what is being sharpened. MOHs hardness is the resistance to scratching. In other words the sharpening material, the wheel in this case, has to have a higher MOHs hardness than that which is being sharpened, for instance the knife. The SG is Aluminium Oxide and is good for regular carbon steels.

In summary the abrasive has to be able to scratch that which is being sharpened otherwise the abrasive will glaze and not cut. It may cut but very slowly and require frequent re-dressing.

If your wheel is glazing then this is an indication that the steel is wearing out the grit in the wheel and is a higher MOH hardness than the wheel and this the wheel is unsuitable for sharpening this particular item.

The SB wheel is Silicon Carbide has a higher MOHs hardness and suitable for high carbon and alloy steels. Silicon Carbide is also suitable for Tungsten Carbide such as you find on some turning tools for instance. CBN and Diamond are harder again and thus also suitable for your harder steels.

I keep the SG for low to mid carbon steels and for harder steels such as special alloy and HSS I use my Diamond wheels but the SB is also an option.

Definitely not. It is a water stone and designed to be soaked in water for best results

I do not check visually. I use the fingernail method which I find more than adequate. Then I use the paper test for a final check.

I do my pocket knives by hand. It takes practice but I get really good results.

It takes practice. I judge the angle by starting low then raising the angle until I feel it grip. Too high and it will definitely round over.

If you use too little compound then it will stop cutting the steel and just rub it. You only need a small amount but you need to apply it often. Every couple of knives I find is best. The idea is that the compound is just on the surface of the wheel. The particles quickly wear smooth, so you need to re-apply often to keep god sharp particles.

Finally, don't apply too much pressure. If the compound is fresh then it will do the job for you. If it is not then you can be tempted to apply too much pressure thus causing your round over.

Practice these skills and you will go much faster with time.

I found mine on AliExpress. I just searched for hand held digital magnifier.

I was watching BigClive's electronics channel on You Tube and in a recent video he was using this electronic microscope. I thought that it might be handy for sharpening so I bought myself one. It cost about $26 Australian including shipping.

Here it is looking at the micro bevel created using a 5000 grit shapton stone on my Narex Richter chisel.