Those are some pretty nice stock funds in your 401(k). VINIX is an S&P 500 fund, meaning only the largest 500 US companies. To approximate a total market fund, buy VINIX and the BlackRock Extended fund in an 80/20 ratio.
The BlackRock MSCI EAFE Equity fund is an international stock index fund. Whatever percentage of your holdings that you want in international stocks can do just great there.
I don't know much about the lowest-cost bond fund in your plan. Its expense ratio is reasonable, but you may want to hold bonds in a Vanguard account to do even better.
So just to clarify; the general recommendation is a 90/10 split (90% stocks/equity and 10% bonds). For your suggestion, that 90% would be divided 80/20 with VINIX/BlackRock Extended Fund (and as comfortable with a % possibly to international funds). Then the 10% bonds portion into the low ER bond choice or into a Vanguard fund?
Yeah, this is basically right. The stock/bond split is something you'll have to decide for yourself. More stocks means more volatility, but likely more long-term gains. If you're comfortable with some ups and downs and won't panic sell during the next stock market correction, 90/10 should work out fine. If you want to play it a bit safer, use a higher percentage of bonds.
Within the stock market allocation, you'll want to pick a domestic/international split. For reference, Vanguard's target retirement funds do about a 2:1 domestic/international ratio. Then the domestic part can be split 80/20 between the VINIX and the BlackRock Extended to simulate a total market fund.
Or you can just put it all in Vanguard's Target Retirement 2050 (or whatever sufficiently far-off year) fund. You'll get roughly the same asset allocation with less to think about in exchange for about a 0.1% higher expense ratio. Up to you.
Over all, back to my original post, what I am looking at then is putting all of my ~$8k annual income from the reserves into TSP.
If you're worried about making your investments too complicated, I might recommend going with only the 401(k). That 401(k) has some good low-fee options, the fees in the TSP aren't that much lower, and you won't need to worry about coordinating contribution amounts between two different paychecks to make sure you get very close to the limit without going over.
If you do go with the TSP for part of your annual contribution, that's a signal that you're willing to put in some effort to shave off small fractions of a percentage point from your expense ratios. If that's the case, go all out. Focus on the bond, small-cap stock and international stock parts of your allocation in the TSP.
For S&P 500 funds, VINIX in your 401(k) has a 0.04% expense ratio, while the C fund in the TSP has a 0.028% expense ratio. This is only a 0.012% difference (really somewhere between 0.007% and 0.017% difference because the TSP uses more significant figures than Vanguard). On the other hand, your 0.16% bond index fund in your 401(k) is higher than the F fund's 0.029% expense ratio by 0.131%. Your BlackRock Extended fund has a 0.12% expense ratio, while the equivalent TSP S fund has a 0.029% expense ratio. That's a 0.091% difference. Similarly, the TSP I fund's 0.029% expense ratio is lower than your BlackRock international fund by 0.041%. Start with the highest-difference fund (bonds) in your TSP. Then go with the S fund, then the I fund if you still have more money to invest.