I would say the biggest thing would be to decide on what kind of bags you want for carrying the gear. I sold a perfectly good full-sus frame to buy a hardtail for bikepacking…turned out there was a 3 month wait for the frame-bag I wanted! I ended up buying a saddle-bag and bar-bag which would have fitted on the frame I sold. 😳 Saying that I now have a small, non-custom frame bag and 2 water bottles fitted inside the frame.
I could comfortably carry everything I would need for three days with this setup…except water. I could soon buy a filter of some sort if I’m going to be away from civilisation though.
Bar-bar: Tent, sleeping mat and sleeping bag.
Frame bag: Mealtime food and a few snacks.
Saddle-bag: Spare/off the bike clothing, stove and a square of bubblewrap for sitting on and for padding the bag out.
Backpack: 3l water, muesli bars, jacket, AA Charger for GPS, phone, small camera, toolkit and a tube (running tubeless though).
1.5l of water on the frame for cooking with. I think a travel tap would suit me instead as I never need more than 500ml at a time.
Here’s a link to lots of different bike setups over on MTBR.