Many of us were excited parents of a relatively skilled 12 yr old; I was two standard deviations on the really excited side. So, I merely give give a perspective of one who lived it.
"to gage his ability against some nationally recognized 12u peers"
This is the kool-aid served by organizations designed to suck money from families. Whatever a kid is at 12u is absolutely no indication of what he will be at 16, much less 18. Some kids will be 6' 160 lbs of undeveloped goo, some will be 4' 6" and 85 lbs. of wiry sinew.
"OR join a local 14u team with the roster of all older kids but may not be as successful or may not travel as far to seek out the best competition in their age group?"
Jumping ahead to recruiting: colleges recruit players, not teams; no one in recruiting cares about a HS or travel team's record or strength, they care about your son's individual baseball skills. If your son is a position player, there will come a time where he needs to be seen against the best pitchers - but that time is much later in the process once he is well into puberty and has begun to develop real strength.
Coaches initially care about two elements: baseball skills and grades. Your entire focus should revolve around those elements because that is very much under your control (much, much later will coaches drill down to other elements such as character, drive, etc.).
There is no size fits all approach to recruiting (when and if it will occur), but the touchstone is baseball skills. So, every action you/he take must ultimately bolster his skills.
My son played NO national or even regional travel ball and never did any showcases even in HS. Until HS he played on relatively weak local travel teams; but, those teams (from 9 yrs of age) had the best coaching (three of his coaches have gone on to be HCs of big college programs), played frequent scrimmage games against other teams (of locally based national type teams) every weekend (usually 2 - 4 games per weekend) through 10th grade.
We spent a lot on individual lessons from competent instructors - batting and pitching. That developed his individual tools. The many scrimmages developed his game tools.
(Ten games a month for years totals up; plus three well run practices a week, plus at least two lessons a week, plus hitting off the tee a few hundred a day. While we spent money, only a couple of hundred a month went for pre- HS team ball.)
We found that the least productive use of time and money were tournaments and meaningful games; conversely the best allocation of time and money were lessons and coaching during practice. (Though the most family fun were tournaments and meaningful games.)
Once in HS, he only played fall scout ball - pitching basically a couple of game innings a week during fall - and on a summer developmental team his personal coach ran just to give players game experience (there were something like 30 pitchers and a like number of hitters on the team). The team played upwards to 10 games a week, no one cared about the score, used real umps, each pitcher throwing a couple of innings. No high pressure; lots of translating lessons into game situations. That system produced literally dozens of pro players and well over a dozen current MLBers.
So, while there is no size fits all, I'd suggest the touchstone be developing individual baseball skills AND academics (see other threads for that). The rest is up to the family and budgets.
Ours was just the opposite. Played on top 10 national team from 9-14 then joined two other top 10 national teams through high school. Played travel ball until high school and played 9 months out of the year, but he also played football and basketball. Son played all the big tournaments from 12U up through high school and lived at Lakepoint it seemed like. Started all three varsity sports all four years in high school and played all summer and full fall schedule. So as Goosegg says no one size fits all. People talk about burnout but that does not include everyone. People talk about playing too much but that does not affect everyone the same. People talk about throwing too much but that does not affect every the same. You will have to figure out what works for your family, your checkbook, and your son. He could decide tomorrow that he doesn't like this sport and there is nothing you can do about it.
Have a plan but you know what happens to the best laid plans. Most importantly enjoy the ride. It ends quickly.