This time of the year, sexual identification shouldn't be to much of a problem, the males should be in their breeding colors. Having said that, overstock if you are going male. They will be more colorful, although more agressive. If your going this rout, keep all males, about the same size, and do 6. Lot's of action in the tank, but make sure there are plenty of structure to break up lines of sight and to provide the subdominate males a place of retreat. The other option would be to go with ONE male, and 3-4 females. Less color, less action, more peace. You could of course go with all female, but then you would be missing the color.
Pumkinseeds can be very agressive. I've had several, and they all displayed varying degrees of aggression. One 6" pumpkinseed killed a 14" bass in my tanks. Overnight from introduction, beat the living tar out of it. Then, the two that grew up in my 55 with a larger bluegill don't pay him any mind, unless he shows aggression towards them. Then, they woop him. Given my experience with these fish, do one of the above stockings. If you wanna experiment past those recomendations, feel free, but I have been keeping pumkinseeds for about 20 yrs now, in all kinds of combinations.
The catfish thing could work, but most bullheads would outgrow a 75. You would need to consider upgrading to something bigger for them. Way bigger. 24" width is what you would need.
I've kinda specialized in centrarchids, if you have any more questions, please feel free to ask! Also, we want picks when you pick em up!
Use worms, squeze down the barb on the hook, and have fun! Collecting your own natives is the coolest way to keep fish. I have my sons first fish ever in one of my tanks, that bluegill means alot to both of us.
