You can use the One World Alliance Route Planner to get a rough idea of prices rtw.oneworld.com/rtw/
Usually you have to travel one way.
Jet Lag is worst if you travel East, but flights are often cheaper in that direction.
Book the major long haul flights with a global alliance and then book shorter domestic flights with local companies - use a travel agent in that country as as soon as they see a UK VPN prices go up for the flights.
If you are travelling for an entire year you can pack a box of winter/summer clothes and have someone send it part way through if needed - relatively cheap to do with a student company and you can return the clothes you don't need.
Look at some overland options (trains, buses) along the way - really, really fun way to travel between places and minimises costs (and environmental impact).
Travel insurance - an absolute must - go for the very best you can afford.
Mix up your accomodation levels - nice hotels are nice, but so are more budget end places, and tours with budget end places tend to be a lot cheaper as well.
I've done a few with work - for work reasons - and one for travel and research. My suggestion would be to go for as long as you can even if it means WFH whilst abroad (if that is an option) on some days, and get off the beaten track in places too.