Here are the highest scores I can do with a custom Sokoban board (Modern Only)
5 ---- 6 ---- 7 ---- 8 ---- 9
5 13 -- 22 --- 32
6 22 -- 65
7 32
8
9

5xN will always have at most 1 box from what I found so far [ 5xN where N is 7 or more is (N*10)-38 ]


-(-)-(-)-()-()-

Level 2 - 50
Level 3 - 110
Level 4 - 180
Level 5 - 260
260 + 90 + 100 + 110 + 120 + 130
260 + 110*5
260 + 550
Level 10 - 810
810 + 160*5
810 + 800
Level 15 - 1610
1610 + 210*5
1610 + 1050
Level 20 - 2660
2660 + 260*5 + 310*5
2660 + 295*10
2660 + 2950
Level 30 - 5610
If you were to get first solve + first place everytime, it would take you 281 levels to get to Level 30