I suppose I had better start doing my homework!
I know that doing 3D printing for the structure has advantages and disadvantages - and yes if I am not very careful in how I structure the infill of the shape of the vehicle it will either end up very heavy with lots of infill, or very weak structurally with very little infill, and that might mean a heavier overall vehicle. What your saying about the heavier payload and more lift problem I suppose means I'd need a larger wingspan to provide more lift as well as a more powerful engine than I might otherwise need in turn.
I should probably point out that I am not very interested in using any kind of off the shelf (or digital shelf) plane body - as I would really like to experiment with building the shape and printing it - even if I do base the shape on an existing wing shape to try and use a more proven design rather than one of my own that might not have ideal aerodynamics and such. I think that while 3D printing the body may force a higher weight, it also allows for rapid prototyping of the shape of the plane. If something isn't quite right for fitting the internals, I can make adjustments and print the sections which need to be replaced. I suppose its fair to say that by printing a design I can make sure its *just* big enough to hold all the internals tightly, with no wasted internal space.
The printing and designing part is probably most of what has my interest in making an RC vehicle at all, I guess I am just a creative minded person and have less interest in reusing the wheel someone else made, and more interest in reinventing it haha.
And yes you may be right, and I'd be lucky to have it lift off the ground let alone be able to maintain flight for a long period of time. I suppose I'm very impressed with youtube videos like "RC Endurance build explained" (I can't post links, url ends in watch?v=nZkzJSkzte8) and I think it would be really cool to try and get results like that out of a fixed wing craft on all electric power - and even cooler if I design and build the thing myself!
So I guess the main point though - your saying that regardless how many batteries you put into parallel it really shouldn't matter from a standpoint of instantly frying the electronics or something like that? Would it make more sense to go and get a bunch of 18650 cells and solder up a pack myself that meets a certain spec? I really don't wanna risk that as I figure it can be trickier than just wiring existing packs into parallel... But then again I've seen some of the guys doing that sort of thing to maximize their range.
As far as heat damaging the electronics from being operated too long, I wonder if having a port or duct to pass air through and over the electronics would help with that? Is that pretty standard? Might not be great for a sudden rain popping up :X
Anyway thank you for your input, I'll consider all these and try and decide what the right thing to do is!