As is with the normal stick, the OT comes in two boxes (base and grip with OTA) with the grip already mounted to the OT adapter. You do not get the normal stick adapter if you buy the OT as a unit from VKB, so going back to normal stick mode is not possible without getting the normal adapter first. The boxes should contain everything, including the tools you need, in the box, so you're good to go. There are comprehensive assembly and installation guides available on their Youtube channel.
It comes with medium springs preinstalled and both a set of light and heavy springs plus two spares of each, and it took me a few iterations to find the right springs and clutch pressure so the weight of my hand doesn't constantly push the OT out of center.
You don't need any software unless you plan to (re-)program any functions - which you will eventually. I think my OT came with the analog stick in hat mode as default, this is one you might or might not want to change. I use my sticks without any curves except for the left twist, which I put a pretty aggressive curve on (see below)
As always, save your bindings and be prepared for the rebinding nightmare. If you launch Elite and have your old throttle not connected, Elite will not load your old bindings file because it contains a device that is no longer present. My solution when switching from a X52 throttle to the OT was to keep the X52 connected and to replace every X52 binding step by step until I could disconnect the X52 without Elite throwing errors for the bindings file.
As for how to use it, it took me a while and a few assignment tries to find a setup I liked and that worked with my brain. As of now, I use twist for fwd and reverse thrusters, Y for vertical and X for lateral. I have no SC throttle bound, I have the five presets (0/25/50/75/100) on the right stick's thumb hat (100 is center click) and use that exclusively in SC. I also use them in normal space and use the twist to accelerate or decelerate around the set speed. For that I needed a pretty aggressive curve to make it sensitive enough.
Also, be prepared to flop around for a while while you re-learn how to fly
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That's all I can think of off the top of my head.