Redmine

Hi,
I just installed Redmine and I just cannot find my way around.
I'm not even sure this is the right tool for us.
I'm seeking advice.

Problem:
We need to manage a few large projects. i.e: more than 10 developers each and about 500 Issues (development tasks) to be done each.
We wanted to move away from tools like MSProject because lack of actual integration with mail/SCM/Wiki.

Redmine adds the needed integration for distributed development and offers bug-tracking support.

What i miss is computed dates for start/finish of each "Issue".
I mean: if I decide some Issue needs more work (Estimated time) I would expect the end date (Due date??) to move accordingly and the Gantt chart to reflect the longer "duration", possibly moving dependent tasks along the way.
This doesn't seem to be what happens.

Task length (as reported in Gantt) is fixed and determined by Start_date/Due_date; if Due_date is left blank the task does not show in Gantt at all.

What I really need is recomputing of End_date and, possibly Start_date of dependent tasks when I change the effort needed.

Another thing I was unable to find is a way to customize the calendar (including working hours).

Can Redmine do what I need?
Did I miss something? (e.g.: some plugin)

Could someone be so kind to point me in the right direction, pretty please?

Thanks in Advance
Mauro