It is going to be a pretty big trip. Africa, Asia and North and South America so the wildlife will be pretty diverse. Hard to really nail it down.What type of wildlife images do you make now Ben? What subjects do you like. Mate give the lads an' lasses specifics,more detail,they can help you more. Wildlife is a big field................you possibly wouldn't want the same image making tools or settings for a springtail as you would for say an elephant
From your reply do you have a camera yet? Ben if you don't yet have a camera all is not lost John's second paragraph is your in. you can start this learning curve today and it doesn't need to cost anything Learn everything you possibly can about what wildlife you would like to make an image of. Wildlife photographers call this "stuff" field craft. Go to the places locally you think your subjects might turn up spend hours watching like a hawk be still and quiet. Gradually patterns start to emerge. You can have the best gear in the world but if you aren't where the bird or beastie is you wont make any images of it.
That's where I'd start Ben,ok there is where I did start. the more you know about your subject the more oft you will bump into it. All one has to do then is point the big shiny bit in the right place and press the shutter...simples Ok the last bit isn't ,but you get my point.
all the luck, get low see what happens