If he took a year off of public school, what are the most important traditional subjects he needs to keep practicing so he doesn't end up with a skill gap in high school?
For a variety of answers to this question which may help you and your son craft a personalized plan for the next year's educational and experiential journey, you may wish to check some of these resources:
1) Common Core Standards
for 8th grade and for high school
2) Gifted Homeschoolers Forum (
GHF)
3)
What High Schools Don't Tell You4)
What Colleges Don't Tell You5)
Youth's Highest Honor6) Taking an out-of-grade-level test, such as taking the ACT or SAT early (through a regional talent search or signing up directly through College Board)
In some places, volunteer "service hours" are increasingly becoming a requirement for high school graduation.
Additionally this upcoming year could be seen as an opportunity to become more
well-rounded or pointy.
He says he could see himself doing something music/tech related for a living, but I wouldn't even know what to call that, in terms of what formal education would lead in that direction.
This may be a great time for him to begin researching. One resource is the
Occupational Outlook Handbook, provided free online by the U.S. Department of Labor, Bureau of Labor Statistics.
He reads constantly, writes on his own, and is usually doing something productive on non-school time, if he's not
exhausted.
He may wish to consider entering
contests/competitions, for fun, feedback, and possibly earning awards/credentials.
*He will technically not be missing a year of school, because he will have completed the MS curriculum this year, and will have banked some HS credits, as well. So this is a relatively low-risk experiment.
Although his academic accomplishments may presently be 1 year ahead, some may say that if the EF skills are not addressed and improved over the next year, and if he becomes too comfortable doing as he pleases without setting clear goals and making measurable progress toward them, the risk of him not completing high school may be great.
Am I missing important things?
Document, document, document.

This may include reading lists, goals & accomplishments, service hours, contests/competitions, etc. You may also wish to keep a printed record of your State's current home school laws to refer to in case they change.