Considering a 4-fund portfolio. Thoughts on these index funds/etfs?

I want to simplify and diversify my investments. I am considering moving towards a 4-fund portfolio with a focus on growth, since I am currently 23.

Thoughts on the growth potential, diversity and overlap of these securities?

VTI — 25%
VUG — 55%
VXUS — 10%
TLT — 10%

I think this provides a decent diversification across US, international markets, and bonds with little overlap. Over time I would be increasing my bonds:stocks ratio. Probably to 30:70 by retirement.

I have about $21,000 to work with currently. I am adding ~$2,000/month.

Let me know if you would change or balance anything differently.

Thanks!