My battery selection is very limited at this time. I have a few 3S 1300mAh, a couple 2S, 650mAh, and a 4S 650mAh. I don't think any of them are the right battery for the FT 3D, but any of them might work in a limited capacity. I'm still a lot of flying hours away from launching this one. Hopefully, by the time I'm ready for it, I'll have a better idea of what battery it actually needs.
I had several of the balsa sticks that come with the FT generic build kits. I used one of them for the connecting spar in this build. I don't see why a paint stir wouldn't work. The balsa planks are all about 1/8" thick. IIRCC, I had to trim the width down a bit.