IA+NH+SC+NV is a pretty balanced combination of representative interests, but if you genuinely want to balance regional and racial/ethnic considerations, consider adding 4 more: HI (most Asian-American state), NM (another heavily-Latino state), DC (another heavily-black jurisdiction) and WV (another heavily-white state).
Based on 2020 pledged delegates and simplifying each state's categorization:
WHITE 93 35.63%
BLACK 74 28.35%
LATINO 70 26.82%
ASIAN 24 9.20%
Though honestly, Nevada is almost a perfect racial/ethnic reflection of the country as a whole, so if you want to count each segment of each state according to its Democratic electorate:
56.63% White
19.42% Black
17.38% Latino
6.57% Other
...which is pretty dang close to the composition of the national Democratic electorate.
