Combining Arduino Uno with GSM and RFID Shield

Hi everyone

Yes, I'm very new to this and yes' I need some help.
Here's the hardware currently available:
-Arduino Uno R3
-Arduino GSM Shield
-Adafruit PN 532 RFID/NFC Shield

Here's what I would like to do:
Upon inital startup, a RFID card should be read. Once that is done, the exact ID of the card should be sent by the GSM shield using a text message to a remote number. Also included in that text should be the exact time when that card was swiped.

Questions:
First of all, is it possible to accomplish that using the Uno? Do I need to initialise the RFID shield first and the GSM shield only once the card has been swiped?
Layout: Uno at the bottom, GSM in the middle, RFID on top. I've been trying with some of the provided example codes. Problem is, if I only upload the "read Mifare" code it won't work when the GSM shield is connected. Even if I turn the GSM off manually it doesn't work. What's a possible cause for this?

And if I want to add some timing information to the text message I'd need some RTC module (DS1307)? Is that correct?

I've been searching the forum for answers and I know there's people with bigger problems, but as said before, I've never done anything like this. So all your help is highly appreciated.

Thanks in advance
Adrian

Any help?
Any suggestions?
Anyone?

Thanks a million