The correct sequence of steps in appointing staff for Dinesh's organization providing services to the corporate sector is as follows:

1. Estimating the Manpower Requirements(C):  This is the initial step in determining the number of employees needed and the types of roles that must be filled within the organization.
2. Recruitment (A): Once the manpower requirements are estimated, the next step is to start the recruitment process to attract potential candidates for the positions.
3. Selection (B): After the recruitment process, the organization needs to select the most suitable candidates from the pool of applicants through various selection techniques such as interviews, tests, or assessments.
4. Placement and orientation (E): Finally, the selected and trained employees are placed in their designated roles and provided with orientation to ensure a smooth transition into their new positions.
5. Training and development (D): After the selection process, the newly appointed staff members require training and development to familiarize themselves with the organization's policies, procedures, and their respective roles.