For larger quantities, just remember the rice : lentil flour ratio is 4 : 1
Good crispy Murukku depends entirely on how the flour is mixed with butter then water and how it is fried (temperature). So pay more attention to those. Do not mix water to the entire flour.
Mix small portions at a time sprinkling couple of tbsp of water at a time
Do not press Murukku way ahead of deep frying as the dough dries out and easily breaks when deep-fried
If the dough is too dry, just dip your fingers in clean water and mix again until it comes to the right consistency.
The color of the Murukku depends on the temperature of the oil. For super crispy (not brittle) and white murukku, deep fry at medium to medium-high heat only.
Murukku/Chakli press is sold in almost all Indian grocery stores. I find the turning types less stressful on the hands than the pressing types. If you are having trouble getting the round shape, don't fret. With a little practice you should be just fine. Until then, you could even press the dough directly into the frying pan. Cut off the strands with your fingers when you want to stop.