Running Conduit Through Wall Outside for Electric Car Charging Station

Hello. I am looking to add an electric car charging station to my house for my new Chevrolet Spark, and am looking for opinions on my plan to accomplish this.

Background
I live in Portland, Oregon. Our winter temperatures typically do not drop below 20ºF. Summer temperatures typically don't spend much time above 90ºF or so.

The car charger that I (already) have is a Bosch Power Max™ 30A / 18ft cord (Power Maxâ„¢ 30A / 18ft cord | Bosch Electric Vehicle Solutions). The documentation for this charger recommends a 40A, two pole breaker.

Rough Plan Overview
My electrical panel is located on a wall that is not adjacent to my garage and (I believe) makes the installation much simpler if I go out the exterior wall and run down the side of the house to where the charger will be installed. This conduit run would be located on the north side of the house and would thus never receive direct sunlight. My floor plan and proposed run is shown below:


I currently have an existing run of conduit doing something similar for a heat pump behind our house:


A picture of the outside wall where the run would be made (note the window on the right edge as a reference to the previous image):


Wire Sizing and Type
Due to the 40A breaker, it looks like the minimum wire gauge that will be acceptable for me is 8 AWG. Doing a rough estimate, I believe my total run will be approximately 50-55 feet in length. I remember seeing somewhere that it can be a good idea to upsize the conductors one size when running in conduit. Does this seem necessary? I'd rather spend the extra money on larger conductors now than in the future.

As for wire type, due to this being an exterior conduit run I am planning on using THHN/THWN-2 wire. I plan on purchasing one length of black, one of red, and one of green (all cut to length). This is an example of what I am looking at:
Wire link: http://ift.tt/1dplQIB
Wire datasheet: http://ift.tt/1dplOjQ

Conduit Sizing and Type
I am currently planning on using EMT over PVC conduit. Are there any compelling reasons as to why I should not do this?

Looking at my Ugly's handbook, regardless of whether I use 6 AWG or 8 AWG THHN/THWN, it looks like I should be using 3/4" EMT.

Going From the Panel to the Exterior Wall
It looks like when the existing heat pump conduit was installed they used metallic flexible conduit inside the walls. I would imagine that this would make pulling and/or re-pulling the wire much simpler and am therefore planning on doing this as well. Are there any issues with this?


Looking at this it appears that I could probably add my wires (8 or 6 AWG) to the existing flexible metal conduit and not overfill the conduit. This would let me avoid a bunch of drywall work. I would then have to change the exterior LB to something else (to go the other direction). Looking through the Home Depot website I didn't see anything that would be a direct replacement. Would I be using a junction box at that point? Something like this perhaps: Wiegmann 6 in. x 6 in. x 4 in. NEMA 3R Screw Cover Box-RSC060604RC - The Home Depot

Connection From Conduit to Charging Station
The charging station documentation recommends using a flexible final connection to the charging station itself (so that it can be mounted and removed easier). As such, I am planning running the final loop using 3/4" liquidtight. Would there be a benefit/requirement to put a junction box or disconnect handle at the junction between the liquidtight and the EMT?

Summary
Is there anything that I am missing or making a drastic mistake on?

Thanks in advance for any assistance!

Attached Images

    

Running Conduit Through Wall Outside for Electric Car Charging Station