Hi @Whimm welcome to the /e/ forum. You already saw the install page for your phone https://doc.e.foundation/devices/herolte/install and most of the answers except for a judgment call are on that page, but let’s put them here !
Downloads for the herolte
- /e/OS build : Oreo dev
- /e/OS build : Nougat stable
To understand the Different build types read this guide
Both are showing a similar history of updates, notice , v.0.17, 0.18, 0.19 … at , what, monthly, 6 week intervals. The dev lags the stable, partly due to the stable being held for a while to ensure bugs have been eliminated. The judgement which to choose is a nice one. The majority of users probably use a dev build and it works fine – on the months I am feeling less adventurous I hold off installing an update till I have heard if there are any bugs. It is the sort of question you could toss a coin about, unless the phone was going to be particularly important to keep fully functional, say for work. From the way you say “my old Galaxy S7” I would suggest the dev build.