Hi and welcome to the forum
First issue is the size of tank. An aquarium that is more than 2 foot high is a pain in the butt to work in or clean. Taller tanks also need to be made from thicker glass and a tank that is 5 foot long x 2 foot wide x 2 foot high with support straps and cross members would be made from 10mm thick glass. Without the straps and cross members it is usually 12mm thick glass.
If you go 4 foot high, you are looking at 20mm+ glass and that would weigh heaps and cost a huge amount of money.
Wide aquariums (3 foot) also need thicker glass.
A decent size tank would be 4x2x2ft or 6x2x2ft. You can buy these tanks off the shelf and they won't be as expensive or heavy as a custom made tank (5x3x4ft).
An example of weight, it takes 2 strong guys to lift a 4x2x2ft tank and using 4 people to lift it is safer. For a 6x2x2ft tank, you need 2 really strong guys or 4 -6 average people. I am talking about an empty tank too.
--------------------
You have 2 choices. Either set the tank up with shrimp and livebearers, let them breed and then after a few months, add the bluegills. Or have blue gills and get them onto dry, frozen and normal aquarium foods, and add shrimp and small fish as a treat.
You can breed shrimp and fish in smaller tanks or ponds outdoors during warmer weather. If you get a double tier stand, you can have the bigger tank on top and a couple of smaller breeding tanks under it.
I would try to get them onto normal aquarium foods because they are cleaner and less likely to introduce diseases into the tank.
If you do get livebearers, deworm them and treat them for gill flukes before letting them anywhere near the bluegills.
