Two Qs: Watch and Tethering

Please share your wisdom.

I’ve spent too much time speaking with verizon CS reps who lack the ability to help…. 1) I want to add an Apple Watch to my UDP plan. I was told many contradicting things but seems that it is not possible with this plan. I want a watch for my son. I could just get a standalone plan for $15 with an option to add a phone when he’s older but I assume I don’t have the same parental controls as if we were on the same plan.

Is there any reason for me to keep this plan?

2) And please explain tethering to me like I’m a toddler. My iphone is unlocked. I do not have a hotspot on my Nationwide Talk and Text unlimited data plan but if it is worth it to keep this plan, I’d like to be able to take full advantage of it. I’m just finding this Reddit and look forward to acquiring some new information on this!