Newbie questions -
1) One time purchase - unlike Adobe photoshop, Adobe elements is a one time purchase and you need not buy or upgrade unless you want to?
2) Reinstallation - you can install in two devices and re-install mutliple times?
On both accounts: yes
If you buy direct from Adobe you get a download, so be sure to copy the install file and a text file with your serial number to AT LEAST one external device in case your hard drive ever dies... to a flash drive or external hard drive or write to a DVD
When you have a serial number program you need to DE-activate before you install and activate on anything after the 2nd activation
One additional caveat:
You are buying a licence for the current version of Elements and your computer must meet the system requirements for that particular version of Elements. Should you update your operating system or computer in the future and find that your version of Elements no longer works, you will have to buy (at a discounted upgrade price) the latest version of Elements.
If you're a Windows user this scenario is unlikely to occur, but if you're on a Mac this has happened in the past.
And more about Windows and operating system updates
I have Photoshop Elements 11 which I initially installed on Windows 8.1 and still use after Microsoft's free upgrade to Win10
I have/use Premiere Elements 2021 and also have Photoshop Elements 2021 (bought DVD from Amazon) but I've just never gotten around to removing version 11 to install 2021 since my picture editing needs are VERY simple, and version 11 does what I need
Windows 10 Pro version 21H1 OS build 19043.1081