You're welcome! Having a car is always a bit stressful but I'm glad to hear that you will have access to parking near the apartment you have chosen. So much easier.
Get a good GPS...you are in the absolute heart of Prague. Traffic isn't horrible but, being an old city, the streets go every which way and you can't just go around the block if you miss a turn! Keep your passport and IDL on you in case you are pulled over by the police for doing something illegal by mistake...I know from personal experience. I got pulled over for accidentally driving in a bus/tram zone...once he saw my passport he let me go but I have never been so nervous in my life!
650 per day is about 26 American dollars per day, give or take...totally worth it! The exchange rate right now is amazing...even touristy Prague is quite cheap. For every 100 koruna it's about 4 US dollars. When I was there last summer 1/2 pint of beer was about 35 - 40 koruna. The cheapest I saw was 29. Your money will go far!
You're staying in a great part of the city...enjoy your trip!