Without knowing much of the specifics of your project, you should be fine with only DX12. Here is from the steam hardware survey:
| NOV | DEC | JAN | MAR | |
|---|---|---|---|---|
| DirectX 12 GPUs | 90.68% | 90.26% | 90.37% | 94.47% |
| DirectX 11 GPUs | 1.61% | 1.65% | 1.66% | 0.85% |
| DirectX 10 GPUs | 0.94% | 0.96% | 0.95% | 0.51% |
| DX 9 Shader Model 2b and 3.0 GPUs | 0.02% | 0.02% | 0.02% | 0.01% |
| DX 9 Shader Model 2.0 GPUs | 0.00% | 0.00% | 0.00% | 0.00% |
| DirectX 8 GPUs and below | 6.75% | 7.11% | 7.00% | 4.16% |