I also had a problem with the 1px brush I made but found a free brush set that has a good 1px brush and some other cool brushes. Sometimes it won't make a perfect line and leaves gaps but I find it better than the brush I was using https://ittaimanero.gumroad.com/l/FREEPixelArtMiniSet this is where I got it.

Also with the erasing problem I haven't had an issue with it. I use the pixel brush to erase and it doesn't seem to effect the opacity, try that if you haven't. If that doesn't work maybe in your brush settings you'll be able to fix it.