ok, I'll try to keep my advice simple.
first off, your panther needs more then just crickets to be healthy and happy.
try to buy silkworms, hornworms, butterworms, and superworms, as well as crickets. (all are easy to buy online, and in some cases, all from the same place.)
buy 3 week old crickets, say 200 or 250 at a time. with other feeders, this will last you a month before they get too big or die off.
feed off the largest ones in the first week...yes you'll get some 4 week old in your batch.
feed 8 to 10 per day...I split this up into two feedings while they are young, but you don't have to if you can't.
by the following week the 3 week olds will turn into 4 week olds and be the size you need. again, 8 to 10 per day.
by the 3rd week, the smallest crickets will be turning into 4 week olds...yes you'll get some small ones as well as big ones.
again, 8 to 10 per day.
by the 4th week most of the left over crickets will be about 5 weeks old and if fed off you should cut back a little, say 6 to 8 per day.
they will start to have wings at this point but should still be small enough to never be a problem. if they all have full wings (6 week olds) I personaly would not take chances in feeding them.
you can go to one of our site sponcers called mulberry farms and buy everything on the list above in one shot.
ask for baby hornworm and baby silkworm cups. also buy some superworms, say the 1 1/2" size, and some butterworms (no size needed). don't forget to buy 2x 100 count 3 week old crickets.

total cost should be around $60 - $70 with shipping.
that may sound like alot of money, but if you got everything from different places, the price for the feeders will be cheaper, but the shipping costs from all the different places start to add up to more money.
as you learn more of how to care for all the types of feeders you can then buy from forum members who will charge alot less but are never as good as the pros...sort of "you get what you pay for".
I hope that helped. if you have any questions just ask here or send me a PM.
Harry