That’s the nature of wireless. Latency depends on many more factors and can vary a ton. If you depend on stable ping, t mobile may not be the best.

both units are very old. the router is a wireless N unit from 2012 that doesnt even support gigabit (needed for 200mbps speeds) and the modem is an old docsis 3.0 8x4 unit. You would be best off buying new of each if you want to actually see 200mbps or higher. Comcast is annoying and they only allow 100mbps upload on very select modems, only four to be exact, the hitron coda, hitron coda56, arris g54, and the netgear cm2050v. If you dont chose one of these, you will be limited to 10mbps upload. All are very expensive, except the coda, which can be found for 90 dollars on amazon. It would depend on your budget on what router you can get, but I would pick the tp link ax3000 which is 99 dollars on walmart.

You should be fine. You generally just want to avoid running it parallel when possible, and to my knowledge 90 degrees is fine. I run a 50 foot cat6 utp cable across a few 120v lines 90 degrees and it sustains a 2.5g link no problem.

This is just current activity, not link speed, available bandwidth, or any real measurement of your max connection speed. This looks normal.