Hey fellow shavers

I have been shaving my head with an electric head trimmer for a few years I have diffuse hairloss on top sides and back and although I'm not sure if its mpb or hormonal... I decided to shave it off and wait it out to see if it every comes back.
But using an electric shaver although convineint they do have a tendency to tug the hair and sometimes pull them out and I've tried rotary/foil/guard ones etc...
So thought i'd give the manual one a go and see how it does.
But I need some advice after my first go.
1) i bought a mach 3 which comes with a few replaceble heads and it says for up to 54 weeks shaving or something along those lines.... how do you know when to switch from one head to another ? i don't want to leave it to late to the point the dull blade starts tearing hairs out instead of shaving them off.
2) using shaving gel was nice but once the hair mixes with the gel trying to remove the hairs from the blades is a nightmare even using a high power shower head took a while... can i shave with just the razor and water to keep the scalp lubricated or do i need to use the gel ?
3) i read only to shave with the grain and i stuck to it only going side to side but never against the grain.. but no matter how much i went over certain areas there was sand paper like stubble left compared to other areas that was slick bald, i had to give in and go against the grain to get rid of those pesky thicker areas i imagine is this okay ? why should i not go against the grain ?
4) and finally i have a massive mole at the back of my head i cut and its still bleeding as i write this... the bugger is big and sticks out i wish i had actually lopped it off as it ruins the look and looks ugly as hell sitting there but unfortunetly its still there and bleeding, any tips for safely shaving over it... or removing it diy style.