The biggest thing you have to worry about is sensitivity to temperature changes. This is a huge problem for minnows.
Have you ever bought minnow from the bait shop like crappie minnows, shiners, chubs or Red-tails? There water is usually between 50 to 60 degree's depending on the bait shop.
Ever notice that when you bring them down to the boat and dump them in the water in your live-well then start recirculating the water thinking you are helping them out with fresh water and aeration. Well unless the water in the lake is the same temp as the water in the minnow bag you put the minnows into shock and some may die. Or even all of them.
So besides dechlorination of the water in a tank watch the water temps. Especially for minnows, the water in the tank or live well need to be within a few degree's. 3 degree's is a good limit to follow.
So floating the bag of minnows is key. And if they are not in a bag and in a bucket take a cup full of the tank water and dump it in the bucket and wait(10-20 minutes). the time really depends on how far the water temps are apart. The more degree's difference means more time to wait.
Then keep doing that until the water temp in the bucket is close to the temp in the tank.
Some are saying dang that is a lot of work. Well with the price of minnows now days(example..$9.oo for a 1/2 dozen red-tails) I think it is worth the time.
The key is gradual temp change. So for putting minnow in the live well. Dump them in minus the lake water. Let them sit in the bag water for 10 to 20 minutes. Then turn on the live well for lets say 2 seconds. Just adding a bit of water to the existing water and let that sit for 10 to 20 minutes. Keep doing that process until the live well water is close to the temp of the lake water.
You will have much more success with keeping your expensive minnows alive.
Another way to do it is fill your live well with lake water and add ice and cool that water down and float the bag in that water. This is the better way of doing it being that the minnows prefer the cooler water and it adds a lot of oxygen to the water. This can be a much more gradual warming of the water which is better. (This can be more expensive way of doing it if you have to buy ice.) I prefer this method.
It also doesn't hurt to add a stress coat to the water. You can buy it at any local pet store. Even the big chain sporting goods store have these types of chemicals.
As for the bullheads I have done 30 to 40 degree water differences and they get well Upset!! But usually are fine. I have not lost one yet doing that. Tough little buggers.
This is way more info then anyone would want to know. Sorry I used to own a fish tank maint. service.
Just my $1.25 worth.