I can to implement change for standard and custom fields?

Summary:

I need to implement change for standard and custom fields like this:

1. Custom fields:

For the fields Commission start date and Commission end date, it is necessary to implement control, in which the system does not allow selecting previous dates, the fields are customized in the header of the expense report.

2. Standard fields:

Regarding the Date field, it is required that the system take today's date by default and not allow the user to make any changes.

For the Start Date and End Date fields, it is requested to implement an improvement that does not allow selecting dates prior to today.