I'd go for the latter... be aware: you have to expose your js, css etc, to be copied/symlinked into public. See http://www.silverstrip.es/blog/ss4-replacement-for-good-ol-themedir-or-loading-themed-resources/
While I'm here - is there a good doc anywhere that highlights key differences between 3.x and 4.x ?
I've looked at upgrade notes - but I'm kind of looking for a "if you're used to 3.x here's what you need to know" type of guide
hmm, upgrade docs are pretty good, with old code and new code. There is also an upgrader tool that gets you started, https://github.com/silverstripe/silverstripe-upgrader
@Alessandro Marotta has joined the channel
if there isn't db details in config.php, and there isn't a __ss_environment.php file, is there anywhere else a SS install will look for those details?
SS4 has .env or Environment Variables, but afaik that's it