1) I'd recommend, if you want to play at 1920x1080, that you use at least a resolution downscale of 1.5. If you're on an 1920x1080 monitor, a resolution downscale of 1.5 will give you a stream in 1280x720 quality (or 720p, which is still HD). It'll put less of a strain on your CPU, and using a resolution downscale of 1.25 will give your stream a rather odd resolution (1536x864, or 864p) that's not much better than what you'd get with a resolution downscale of 1.5. Also, the FPS you're streaming at puts a strain on your CPU as well. Most people stream at 30 and it looks fine, but if your PC can handle it, you could try streaming at 45 or 52 fps (because apparently there's minimal to no difference from 45-52fps up to 60fps).
2) Even if your upload is really good, if you make your bitrate too high, people with a download speed less than what your bitrate is set to will struggle to be able to watch your stream. From my experience, you can have a perfectly clear stream with your bitrate at 2000 to 2500 kbps, so even if your upload is significantly higher, making your bitrate higher just makes it more difficult for those with worse internet to watch.
Also, quality options will come in when you're not partnered when you have a certain percentage of all of twitch's viewers. I don't know what exactly that percentage is, but it's typically easier to get quality options later at night when less people are streaming (I've gotten it as low as 40-45 viewers), rather than in the day where it usually takes 100+ people watching in order for them to be enabled.