Multiple shields on Arduino Mega 2560 / General Project feasability

Projects General Guidance
1

Hello everyone,

Evaluating what kind of hardware I will use for a new project and one option is the Arduino Mega 2560.
HOWEVER: I'm unsure whether it will do what I want it to:
I will need connectiviy to:

2 different RS232 devices
1x one-way from a GPS,
1x two-way to another mC
Both are "real" RS232 voltage levels as far as I know at the moment ....

1 ethernet connection to a PC

So I have the following questions:

I've seen there are shields for Ethernet (Arduino) & RS232 (cutedigi) ... I am however unsure whether it's possible to connect multiple of these shields to the same Mega 2560 board. Is it?

Is it possible to actually do some stuff on the board between all the "communication" tasks?
Or am I just always waiting for the next incoming signals?
Because I would like to board to do some control stuff for me ... basic idea is:
GPS signal from GPS controller
High level control i.e. setpoints from Ethernet (PC)
Do control onboard
send control signals to other microprocessor, get feedback loop with signals from other microprocessor

Is something like this feasable?

Thanks for any help

2

The official ethernet shield uses pins 4, 10, 11, 12, and 13.

You'd need to post a link to the RS232 shield, so we can see it's pin usage.

Is it possible to actually do some stuff on the board between all the "communication" tasks?

Depends on what communications speeds, the volume of data (number of characters and number of times per second/minute/hour/day/week), and what else you want to do.