I don't quite understand what you are trying to say.
The 1N400x series is rated for a maximum of 1 amp. The last digit denotes the maximum forward voltage the diode can withstand.
Yes, but you will need an external power source (like a 9v battery) and a current shunt. If you have a multimeter just set it to Amp mode and put the test leads in series with the test load. Its easier this way.
I use Efest 18350 cells for all my C6 builds. It fits just perfectly. It sticks out of the battery tube by about 1mm but the tailcap will fully close without much effort.