Honestly, depending on the usage scenario, this would be a downgrade as the Ryzen 3 3100 is already based on the newer Zen 2 and offers better single core performance than the 2600X.
I would first wait for the new Ryzen series. Your system is not that old. An update of the components mentioned would give you a good performance boost, but in my opinion nothing earth-shattering in real-life applications.
to avoid a full reinstall a syspray, which implies uninstalling all drivers before doing the syspray and of course backing up the data on a safe media. syspray would be the easiest. even if a clean reinstall is better.
Well, you can buy the tray version. But that doesn't make any sense. You don't have a fan, but you also don't have a warranty on the tray version. In addition, the boxed version is cheaper than the tray version.
So it's better to just buy the boxed version.