I have never been to a cosplay event or anything, but as to the keyblades I suggest pine, a jigssaw/dremmel, and a Pucking big amount of time (summer heights high reference!). get an image of said keyblade, blow it up in paint/photoshop/whatever, print it out and put the peices together, blu tac it to the pine, trace and cut out. probably about a days work for the more intricate ones(i.e oathkeeper, kiary's keyblade, ultima)and then hang it from somewher and paint. probably also a good idea to make the handle nice and round, or wrap it in something soft before painting, and most importantly, make sure you can carry it around for a day. Unfortunatly I forgot that with my Terra's keyblade and it is massivly top heavy.
My personal opinion is that vens keyblade has a yellow hand-guard-thing, a dark gray lower "stalk" which changes to lighter gray near the top. i painted my cosplay one as such:
View attachment 1427
i can tell, because if you look VEEEEERRRRYYYYY closely at the join between ven's hand-guard and the holdy-bit, you can see a tinge of yellow.
