Welcome!

Quote
our son was RIAS tested with a composite score of 150... I see a future stretching out in front of him that could be really fantastic or really painful, depending on the environment.
Parents are large part of that environment.

Quote
His vocabulary is lacking compared to his peers in school... he doesn't hear tons of dialog at home that other children would - day to day chatter is just nominal in our household.
You may wish to provide him with an enriched environment by speaking with him more and/or facilitating more conversations amongst family members for him to overhear and/or read more selections which may help enhance his vocabulary.

Quote
I'm not terribly educated on what to do with a PG kid.
You may wish to do two things now while your child's needs are fairly straightforward and comparatively easily met.
1- Read up on advocacy as there may not be time to do so later when life may call upon you to be prepared with advocacy knowledge and skill to assist your child.
2- Focus on your immediate family as the first place your child's needs are recognized and met. For example, the vocabulary you mentioned previously. Parents often share how much they have stretched and grown and changed to provide an enriched environment which supports their gifted child's voracious appetite for learning.

Quote
Have I gone off the deep end?
Possibly you are exhibiting gifted intensity and overexcitabilities?