If it's in your budget, then I would try to hit the maximums for the 401k and IRA. You can invest in index funds within an IRA, although the 401k options may be more limited. I would say using tax advantaged accounts is even more critical if you're trying to retire early, and it's great that you're starting early to maximize the time spent in market. You might also check out r/FIRE for more early retirement planning.

I would put more in your 401k or open a Roth IRA. The 37k is probably enough or maybe too much for an emergency account and so the $1000 after tax per month could be put in other areas. The PF wiki could be helpful!