Heres a tip that is handy sometimes, screw the nuts/bolts loosely back into whatever it is that you have dismantled in the places they came from. It saves heaps of dramas later on. Bag and tag is a good idea as well.
Mook I am sure the flex plate bolts would be similar to the flywheel ones which are fairly thin through the head of the bolt. They will probably have a Y style marking on the head of them indicating they are high tensile bolts. As for actual length you bay need to suck it and see if you are not sure.