The big deal about capacitor discharge and voltage is that not everybody knows what they are doing and why it has to be done in certain ways sometimes. Not their fault, they just haven't been trained. Because of this they may injure themselves and they could also create more damage in the appliance.
They think that electrical/electronics repair is easy. "It's probably only a fuse", simple. The litany of problems caused by DIY repairs in this forum is proof that it is not as simple as it sounds
Shorting out a high voltage capacitor incorrectly could possibly lead to sparks flying causing flash blinding. If not using the appropriately insulated tools could lead to electric shock and depending on the person's medical condition could even be fatal.
One example that I've seen is a screwdriver welded across the capacitor terminals because it wasn't big enough to handle the current flow and melted. They just heard "short it out with a screwdriver" and grabbed the first one to hand. As you can see what may be obvious to you is not necessarily obvious to somebody else.
The correct way to discharge a high voltage electrolytic capacitor is to connect the +ve terminal to chassis Earth via an appropriate high value resistor (MegOhm), with the correct power rating. to limit the amount of discharge current flow. Then when satisfied that it should be mostly discharged apply a s/c across the terminals to doubly ensure that it is.
Sounds unnecessary but not only is this the safe way to do it, it also prevents possible damage to the capacitor due to high surge current flowing.
It only takes a few minutes but I guess impatience wins out, hence the screwdriver
The fact that you can get away with using a screwdriver is testimony to the robustness of the component but again all are not equal.
To my knowledge there is no "standard" diode for microwave ovens.
I would have thought that their rating will differ depending on the design of the circuit.
I'm not in the repair business and have only replaced 2 diodes in my time, whilst fixing microwaves as a favour. More often it is the turntable drive motor or the control panel that I've had to deal with.
I just used what the microwave oven manufacturer listed in the parts section. After all they know their product best.
As to the price, once you know the diode specs (or type number or equivalent) you can search online to find suppliers and also the manufacturers (brand) of the diodes. (Try mouser.com, farnell.com, element14 -I'm sure you have your own preferred suppliers). Knowing the manufacturer (brand) is sometimes helpful as you can then check their "reputation" to see if their components are quality products or just so-so, This used to be the case with capacitors as you're probably aware.
It may be that it is better to pay a bit more for a part if you know that it is going to last the distance rather than have it fail prematurely because the quality is not there.
Sorry that I cannot be of more help.