A lot of great suggestions above by others with common, opposing and divergent solutions, I couldn’t disagree with many except for saying beware of an undisciplined take all in the kitchen sink approach then work out the pack size, well how’s a 110L and 40kg worth pack sound
It looks like the OP is a beginner, wanting to get into other hikes and the gear will be used for future trips and worth getting the right gear to last but not overboard on expense. There are a lot of websites on how to manage a good pack base weight that suits you such as
https://faroutguides.com/how-to-calcula ... se-weight/Generally less should more without compromises comfort and safety as you don’t want to weigh yourself down unnecessarily affecting the hike enjoyment or cause physical exhaustion problems to the point of failure or worse.
As a beginner at least aim in between for lightweight category under 9kg base weight pack, includes everything except food, water and fuel, which then comes up to around 16-17kg total. You can go slightly higher or lower but try to avoid fully loaded pack towards 25kg and over for a 5 day Overlander hike, which is not a very extreme or long hike and where water is available. You would probably need a budget around $1-2k to achieve this, much less if second hand good condition used items can be found in Gumtree or here as you have time to gather and refine them 12 months out.
For example, among the basic items they should be around or under 1.8kg (<1.2kg) for 60L pack; depending if you are a warm or cold sleeper a down fill sleeping bag say -2 or -5C rated 1kg (<0.6kg); tent 1.7kg (<1.2kg); mattress 600g (<400g); cook set 500g (<300g); other doing the same items, clothes etc if you get the idea. However, if you ignore the weights and go all out kitchen sink approach it will easy double or triple the weight very quickly. The weight figures in brackets are suggested easily achievable if one makes further decisions based on available equipment out there and spends more. If you go that way there is already a 2kg saving with those several item choices above, so keep going and it can add up to around 4kg significant weight saving without being ultralight crazy and expensive.
There are previous similar posts about preparing for the Overland hike.