If you include a column that represents duration in days for each
aspect of the project, subsequent dates after the start date could
simply be a formula. The date for each task in the project could be
the date for the previous task plus the number of days for the current
task.

For instance: suppose column A is your task description, column B is
the duration in days, and column C is the due date for the current
task. Suppose the entry in A1 is "Start Date" and the entry in C1 is
1/17/2005 (from your example). The next task, in A2, is "Send first
round layouts", the duration in B2 is 4, and the formula in cell C2 is
=WORKDAY(C1+B2,D1:D10)
.... where D1:D10 is a list of holidays. The WORKDAY() function returns
the date of a weekday that is the number of days (specified in B2)
after a startdate (C1).

By linking each tasks due date to the prior tasks due date, your
schedule becomes dynamic. If a date slips then you can either hardcode
the date or adjust the number of days for that task to match, and
subsequent dates will adjust.