No, not all programing is equal, BUT be careful. "Age appropriate" doesn't necessarily mean neuro-developmentally appropriate. Lots of shows with CONTENT for young kids is really TOO fast on the screen to be healthy. It isn't about the pace of the STORY, but about the quick changes to the actual scene... camera angles, backdrops, random flashes etc. When you watch the show, ask yourself "is this show asking me to maintain visual and mental focus, or to quickly and regularly shift and adjust my focus?" If it's the latter, it's better to avoid for little kids.
That being said, even with my careful monitoring of screens in his early years, DS has ADHD... but he certainly got it honestly, because so do I (raised almost entirely without screens... I mean we barely had until I was in middle school).
To the other part of your question: We set limits on screen time primarily by requiring that DS "earn" screen time each day by getting five "checkmarks." He gets them for chores as well as for things like reading for 20 minutes, doing work in a problem solving book, or being a good sport for his non-preferred activities.
He uses a desktop computer for most of his screen time both for games, websites and watching Netflix... most of what he does you would consider "educational" because that's what he likes.... he plays online chess against other kids, plays a superhero adventure game, or goes on cool-math.
Anyway. We use Microsoft family safety to restrict his computer use so in addition to only accessing specific sites and programs, his user id only gets a two-hours (total) each day, (if he forgets to log out the timer keeps going and he's just SOL later in the day). AND there is a curfew so it logs him off at dinner time regardless of whether he's reached the limit.
The only thing he watches on the real tv is stuff we're doing as a family (mainly Jeopardy! or the news) and there's no time limit as long as he has his 5 checkmarks.