OS/Desktop environment does matter. It is going to be the single biggest thing that competes for resource if you only intend to use the machine for what the OP

OS/Desktop environment does matter. It is going to be the single biggest thing that competes for resource if you only intend to use the machine for what the OP wants. Most websites still work OK on slow machines (my travel laptop was one and it could handle 90% of the websites just fine). OS/Desktop env is often the biggest sink. That machine for example would hit 75% CPU on windows 10 just idling which didn't leave enough room for anything else. Wiped it with Ubuntu + Gnome and it went to ~25% CPU usage while idling. Switched to Ubuntu + XFCE less that 3% while idling. The only website I had a problem with was Patreon.