FWIW most cheap pedals of this type have a tab washer that is meant to allow you to adjust/service the pedal using only a (12mm from memory) socket on the locknut. However the tab washer usually has loads of backlash so adjustment is often trickier than it should be; when adjusting the cone you need to keep track of the relative position of the cone and tab washer else it can take for ever.
In cheap pedals it is not always the case that the inboard bearing has the same number of balls in it as the outboard bearing. However you can assemble the outboard bearing dry, and see if there are the right number of balls in it or not, and then add grease afterwards.
Alternatively if the cups and wear marks on the cone/spindle are the same diameters all round, it is a fair bet that the number of balls will be the same too.
In any event if you tighten the cone finger tight and the bearing still feels like a bearing (not too groinchy) then you probably don't have too many balls inside it.
Obviously if the dustcap falls out of the pedal water and dirt will be able to get in. However if the pedal develops the slightest amount of free play, the locknut can usually touch the inside of the dustcap, which pretty soon causes the dustcap to fall out.