I agree with starting to post now. Build your backstory and start getting followers before the trip. Share budget, packing tips, family pics, previous photos you've taken, etc.
I haven't done blogging myself, but I think you should look into using Instagram to get followers and direct people to your blog. Post cool pictures, use lots of hashtags, follow people and build up an audience who will get motivated to click through to the blog. Use some suspense in the post to get them to follow through and read the rest. If you are using equipment or clothes from specific brands, tag and follow them and see if you can become a brand ambassador for them, I see people posting links with discounts so there may be some money to be made like that.
Also, there are millions of bloggers who don't make much money at all, so I wouldn't go into this expecting to make a bunch of cash, if any. If you are doing this primarily to record your trip, share your pictures with friends and family who want to follow along, and create interesting content, you might end up pleasantly surprised if you also make a bit, but it shouldn't necessarily be your primary goal.