PJL80: I've been growing my hair out since May 2012, when i last had it shaved down to about 3/4" long. It took about 15+ months (at my growth rate at least) to get it to Dude length for PAX Prime 2013, and I had to trim of about 6" in the back to level it all out for ECCC [see pic above] 6 months later. Hopefully that gives you a good estimate for how long it will take, but i'll tell you that you'll get more people enjoying the costume when you have real hair instead of a wig. the hard part is growing past that annoying length around the 8-10 month range before it can fit into a small ponytail. haha
the beard is kind of fun since you might look a bit more intimidating with a longer one (or even get more attention from the ladies). if you do grow it, be sure to grow out some under the chin to get the full effect. The Dude doesn't just have around the entire mouth, but a bit more filled in. check out his profile shots in the opening scenes for some ideas on what i mean.
i hope you find the the sandals in stores. i called around the Seattle area to several places and never found them locally. Chicago might be a bit different, but it's really a craps shoot when doing that. plus, really, the ones you have on the pic will work for a con. i accidentally wore my black Doc Marten sandals all day long during ECCC and 1) nobody pointed that out, and 2) everyone "got" that i was The Dude without them. you'll be fine, i'm sure. just order the Okabashi online and use them for next time. [heh, i ended up wearing my Oakley sunglasses at PAX and nobody pointed it out]
