You can grow with out the meter but I would not recommend it. Ph is way to important to not know what the number is. You can follow the label to mix your nutrients but Ph is another issue. If you don't know what your Ph level is then you are only asking for trouble. Ph papers are not accurate enough to give a good honest reading.

You should do full water and nutrient change every 7 to 10 day's. If the level drops to low in-between a full water change then you just add back Ph adjusted water to bring the water back to normal operating level.

If this is your first grow I suggest you grow a few times with dirt. Hydro is hard enough with the right equipment but to not have the proper equipment you are looking at a disaster just waiting to come to pass.

Good luck, hope it works out for you.