solutions 6(optimised),7minimalist, 8probably improvable
[s>][<>][n^]
--->[^v]
[n>][n>][nv]
level 7
[ ][s^]
[b>][^v]
--->[^v][bg]
[n>][nv]
level 8, 15 parts left over, 0 waste
[n>][n>][s >][v>]--->bs
[b^][<>][n^][<>]--->2s
--->[n>][^v]
[S>]--->S
bold side of splitters outputs first