Thanks so much for the great feedback baudman and JAC!
The most kms I've done in a day so far is 60km, but if I go, I do plan to put in some training and make sure I can go the distance.
Definitely need to invest in some more pairs of good knicks/bike shorts too. I wore a pair yesterday for a 45km ride and it made a huge difference. I also applied some Chamois cream too which must have helped!
I was also thinking about trying some more comfortable saddles. I use a Brooks Cambium C17 Carved saddle, which is OK, and certainly more comfortable than the carbon saddle that used to be on it, but I'm not sure it's 100% a good fit for my sit bones. Definitely thinking about getting a proper bike fit and trying a few different saddles before I embark on this adventure.
Any advice on where to find some good hills to practice climbing in Melbourne? I live in Hawthorn and there are a few big hills like Balwyn Rd heading towards the eastern freeway trail, but inner Melbourne being pretty flat doesn't seem to give as much opportunity to practice bringing on the pain. I guess I could take the bike to Mt Dandenong?
Also, given it's my first time, do you think it's best to start with the shorter variants of the race or go the whole hog first time?