Newbie Help! , Need parts info for a quadcopter

##Motor Directions##
Yes the motors needs to be connected so they are turning in opposite directions as you go around the clock. It’s documented here:

http://copter.ardupilot.com/wiki/initial-setup/assembly-instructions/connect-escs-and-motors-pixhawk/

You have a Quad-X frame, so looking at the top with the drone pointing forwards away from you:
Channel 1 is top right and rotates Counter-ClockWise.
Channel 2 is diagonally opposite 1 at the bottom left also rotating CCW.
Channel 3 is to the left of channel 1 and rotates ClockWise.
Channel 4 is diagonally opposite 3 at the bottom right also rotation CW.

##Propeller Mounts (CW/CCW Adapters)##
Regarding your self-tightening prop adapters you got with the Multistart combo. You use the threads/caps with the opposite direction so they tighten as the motor moves. That is when a CW threaded adapter is on motor 1, it rotates CCW so the inertia/friction/torque of the motor pushing hard to rotate will make the cap nut force itself to tighten DOWN against the CW thread.

You can test this, hold the prop adapter top then rotate the outside of the motor in the direction it turns, the propeller should be tightened. It’s so easy and when you are used to them, you can just quickly spin them down to as tight as your hand can make without too much stress, then let them tighten themselves completely when you spin up the motors to take off. Worst case if you left them lose the props skid a bit until they are tight. but they will never come off.

##Mounting in Frame##
When you build the lower case of the Low-Hung FPV250, leave one set of those red support spacers out, the one in the middle offset towards the back is best, leaving the front bay separated for FPV equipment. There are slots along the sides, to start with use cable ties to mount the board. Later if you can get hold of a 3D printer or order a print online you could mount the Pi and Navio+ inside one of the custom cases posted here:

You could also use only the bottom half of any standard RasPi case if you want a stronger base. With any case it’s probably best to velcro it down as they don’t normally have fixing loops for cable ties. In the long run I’m thinking of modifying the base of the LH to make it fit aound the Navio+ (and even Pixhawk was a squeeze) without removing any spacers and with optional cable tie loops.

##Batteries##
Caution you need to know about Lipo safe voltage ranges. For each cell, it is 3.0v to 4.2v and below 3.3v is “dangerous”, below 3.0v “critical” meaning it may catch fire or explode. Hence the Lipo bags for storage and transportation. In fact your charger may refuse to work with batteries where any cell is below 3.3v (there is a trick to charge briefly up to 3.3v per cell as a NiMH but you’ve still taken some life out of it so want to avoid this). The normal level for the cells battery is 3.7v and the further below this you fly the more stress on the battery.

With a 3S (cell) battery we have the following tables to consider:

Cell Voltage Ranges
3.3v per cell empty (danger)
4.2v per cell full
= 0.9v range discharge (100%)
0.7v range used (80% rule) = warning land now!

3 Cell Battery Voltage Ranges
9.9v 0% empty (danger)
11.4v 20% empty (safe) = warning land now!
12.6v 100% full

It’s all explained here:

p.s. for the Hobby King PDB volt and amp sensor I used these values in the APM configuration:

ArduPilot Battery Settings
Voltage Divider 10.125635
Amps Per Volt @ ~10.86A = 20.5530