The charging issue is honestly the most difficult to overcome, as the tablet draws quite a bit of amperage when the screen is on (full brightness), wifi is on (for tethering from phone), along with BT and GPS.
Luckily for you, the Nexus 7 is known to be very car-friendly as far as draw. My tablet was not.
As far as the USB adapter for a right angle, I found this site while I was doing my integration.
USB Cables - From www.AngledCables.com - Overnight delivery available! - USB Cables
Here's a thread about proper car chargers for the tablet:
The Only Car Charger You Need for the Nexus 7 - xda-developers