The foot nuts are supposed to be fitted/refitted using an impact wrench. It’s not always the case, but you should expect the possibility that, on attempted removal, one/both nuts will just spin. This can sometimes be overcome by having the fork upside down and getting somebody to compress it while you loosen the footnuts – the inside of the cart is pressed against the inside of the lowers, allowing the nut to be removed. Upon refitting, you may find that you’re unable to tighten a foot nut properly.
Oil is by volume rather than height/level. Check yours here.