You will need to begin with 2 or 3 tanks.
Probably the best and easiest way to improve them would be to collect the fry from the females that you already have. You will need a growing out tank for the fry. after 4-6 weeks the Young should start to sex out, you will need to separate females in one tank and males the other carry on feeding a good quality flake food if possible add some live food in their diet. At six months of age most males show full colouration and females will be at their best for breeding. Take your best colour male/ fin shape bred it back to your best female guppy. Also to help improve the Strain is to breed the father back to the daughters, it will take a few generations to fix a desired strain.