RE: Nexstar conversion
A5S set up is sweet for the plane, she can do with a 4S but 5S is better. Just look into the motor. The Great Planes concept is to turn the prop like a glow motor. High RPMs.
For me I would go with a 42-60 motor of about 600KV and then turn something in the 12x8 range. Two reasons ... The 42-60 can later be used for good performance in a 40 or 50 sized sport plane, we all move to bigger planes, and secondly, the bigger prop gives you more thrust at a lower RPM. No point turning a 10x5 at high RPMs. That's my 2 cents.
As for battery access, you can just stuff the packs into the tank area with access from the wing. The area in front of the canopy is rounded, cutting an access hatch may spoil the look. Watch out for CG issues when deciding on the battery capacity, I still prefer 4,500 to 4,900 mAh packs.