Woocommerce Checkout Customization

I need help customizing my Woocommerce site.

Requirements:
- Products should go to checkout without payment options.
- Mandatory file upload before order submission.
- Allowed formats: PDF, JPEG/PNG.
- Custom field: Customer notes.

Ideal skills and experience:
- Proficient in Woocommerce customization.
- Experience with file upload functionality.
- Knowledge of adding custom fields in checkout.