Tonearm/cartridge weight considerations


I have just decided to dig up my old vinyl collection that has been waiting for better days since mid-80s. Bought a turntable (Thorens 124) without tonearm. I have Shure V15V-MR cartridge. Started to look around for an appropriate tonearm and found out that the tonearm/cartridge issue has grown into a science. Now I am confused about this tonearm/cartridge weight issue. Could enyone illuminate me about this issue, mainly covering the following questions:
1) they speak of light/medium/heavy arms, so what are the figures for those weight categories?
2) are there weight categories for for cartridges and if yes - where my SHure V15V-MR fits?
3) does a light tonearm needs a light cartridge, or is it totally opposite - a light tonearm needs a heavier cartridge and vice-versa?
4) what can go wrong if the rules of tonearm/cartridge weight are ignored?
Thank you!
crockusbird
There are a lot of modded/rebuilt cartridges out here, just as there are a lot of modded electronics. I suppose: a lot of people that aren't aware of the practice as well. The rubber cantilever suspension makes all the difference in the "compliance" of the cartridge. Change the density of the rubber, you've changed the compliance of the cartridge.