I'm an amateur, and i want to buy the sony FX7

Now i'm wondering if it is a good decision or not

soms say save some more andbuy the sont fx 1000
But it costs 700€ more then the fx7

How well does the FX7 perform in low light conditions
firework, concerts, night shoooting of low lighted archtecture ( i.e. Paris - sacre coaur, notre dame, eifeltower etc.)

The sony FX7 does not have a XLR-connection for the microphone

Is this a big shortcoming or not

What is an excellent external microphone for the fx7

who can help me out with making the right decision

If you are going to use the camera often in low light situations that you described, then go for the FX1000. The FX7, as you said has no XLR inputs, but you can always buy an adaptor like the BeachTek DXA-4 BeachTek product selection... (http://www.beachtek.com/prod.html)
The built in microphone of the FX7 is excellent but if you want a budget directional microphone then get the Rode VideoMic: Rode VideoMic (http://digitalproducer.digitalmedianet.com/articles/viewarticle.jsp?id=261084&afterinter=true)
Overall the FX7 gives you fantastic pictures all round, although in low lights you need some add on lights.
Minimum illumination figures:
FX7: 4 lux
FX1000: 1.5 lux

Stelios