Advice request - tying into existing basement drain for water softener

[trdrjojo]

Pictures:

https://imgur.com/a/thpdIHK

Hello! I'm trying to figure out how to DIY a drain for a water softener (to be put) in my basement. There is no existing floor drain for me to use, so I think my only option is to tie into the existing drain line.

Questions:

1. Do the layouts in the diagrams work for tying into an existing horizontal or vertical drain?
2. Any opinions on whether it would be easier to tie in vertically or horizontally, or between positions 1/2/3 in the second photo? Or is it purely my preference?
3. To tie into the main drain, is it okay to use two shielded couplings? Or is there a better way? Can I glue one side normally and just use one shielded coupling? I've seen this article on using PVC slip couplings, but worried about how fast you have to work.

Thanks so much for any advice!