The reason I say go into the right size pot is because it cuts out potential watering issues. If you go into a pot that's too big and saturate it, you'll have large areas of stagnant coir, which isn't healthy. There's nothing wrong with going straight to final pots straight away, as long as you're careful not to over water, which it looks like you have been.
One little tip, in future when you're potting up, try and bury as much of the stem as possible, right up to the bottom leaves. Roots will form from that stem and the base of the plant will be stronger.
EC is electrical conductivity. It's just a universal way to measure feed strength with a tds/ec pen.
