https://www.devicespecifications.com/en/model/b01b3bc2
As for which apps to remove and/or substitute I do suggest that you disable, rather than remove, an app or service first, then wait a few days to make sure everything you need still works (some services are dependent on others) before actually un-inistalling it. An app like Titanium Backup includes the ability for you to 'freeze' (disable) or 'defrost' (re-enable) an app or service
Some of my favorite 'root required' apps:
AFWall+ -- a well-developed firewall app that allows you to selectively block-allow each app from any online access.
BusyBox Pro -- a collection of miscellaneous Unix/Linux tools and utilities (this is more of out-of-sight tools app as you'll interact with occasionally, these are utilities that generally run in the background only when needed)
Root Explorer -- feature rich file manager app
SuperSU Pro -- root management utility (another app that you don't interact with too much)
Titanium Backup Pro -- versatile and reliable backup tool and app management
And since you're re-purposing your phone to be a media player, for a good media player app, I like both MX Player and VLC. Both apps can play a wide range of different media file types, much more than the default Android media player app. If you want to dig in and tweak settings MX Player has slightly more options in its settings menu but note that the free version is pretty ad heavy now so opt for the pay-for version if ads annoy you. VLC is ad-free regardless.
As for rooting, an old, secondary phone is really good choice. Rooting a primary phone involves risks if you were to make some kind of inadvertent mistake but now you've got something to experiment and learn with. Plus with an older Samsung you don't need to rely on one of those one-click rooting apps that add in very questionable privacy back doors in the OS.
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