The amount of harvesters you have should really depend on your gameplan. If you are rushing you can go 0/1 miner and sell mcv. For longer games, as a general rule of thumb, you should probably tech on 5 miners as allies/sov or go second war after 4 miners and build more miners/wars from there. Though this can depend on whether there's gems/oils etc.
Mining all of your ore early on is not a good idea. You should also use miner control to make sure you are mining most efficiently and allow ore to regenerate properly.