Do you actually wash cloths while they're in the bags? 🤔
I use laundry bags for moving dirty cloths when traveling, but when I go to wash them, I take them out of the bags.
As for the mixing of lights and darks, I think it depends on the cloths and temperature...
If they're brand new clothes, you wouldn't want to mix them, as colors can bleed more the first couple of washes (especially bright colors like red) and get on other clothing and change those clothing color.
Also the hotter the water, the more likely they're to bleed, or dark colors are going to fade.
Ideally, hot water helps get more smells hot, but also can damage the clothing more, so if they're not too smelly, you could use cooler water, especially to stop dark colors from fading.
Also, this is the catch 22 which gym workout clothing.... a lot of that gear is made out of a material that's good for stretching and moving to give your body more freedom to work out.... but that material also does really bad in hot water and gets older faster.... but since your working out in them, it gets a lot smeller, and one needs to use heat to get more smells out. So I would honestly suggest, maybe not buying the stretchy gym workout clothing if you're actually going to work out hard, but just some comfortable clothes you don't mind ruining with sweat and hot water... and then you can use hot water to get the smell out.
No but if it’s socks, I have a small bag so it doesn’t get lost. You can buy color catching sheets to avoid that. https://www.amazon.com/Catcher-Laundry-Maintains-Clothes-Original/dp/B01B0ADMP8
Nope. As a matter of fact, I would never use a net bag to wash my clothes. They need to be free to remove the dirt and soap when they are spun and rinsed.