With multiple Roku devices, you can either have one account for all or separate accounts for each. The advantage to a single account is that installing or removing a channel from one does the same for all. But that's also a disadvantage, if you want different channels on different devices. In that case you must have separate accounts. As far as the channels themselves, the only advantage I can think of for using a single account is to have your favorites and subscriptions synced to all your devices. Again, if you'd prefer to have them separate on the devices, then you need separate accounts. And for YouTube TV, that means paying for two accounts. Only you can decide if that's the best way to go.
Nvidia Shield, Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.