Couple of questions from a fairly new player (Playing support)

Hello! Been playing for about 200 hours, got around 750 MMR, love playing support (Especially Silencer). Been watching probably equal amount of gameplay, maybe more.

I have some trouble understanding the norms of Dota, relating to pos 4 and pos 5, especially when I started playing ranked. Of course, it is a game of nuances, so there are probably no exact answer to each scenario, but I would appreciate some tips from more experienced players.

#1 Farming: I usually avoid farming unless I am absolutely sure the core aren't gonna have the opportunity to get it instead. But, if we end up losing, some players end up criticizing me for only having a few items? Are they just ignorant or am I doing something wrong? Should I prioritize farming more than running around, as a pos 5 for example?

#2 Stacking: Am I supposed to stack, even if nobody asks for it specifically? I understand certain heros are better suited for stacked camps.

#3 Laning stage: If I can leave my core alone to soak up as much exp as possible, I should leave him alone, right? Then go ward, stack etc. There have been certain scenarios when a core asks me to stack, pull etc. But they also expect me to save them if they suddenly get ganked. What do you guys prioritize, stay in lane or listen to the core?

#4 Difference between pos 4 and pos 5: Is it only pos 5's job to ward/de-ward? Only pos 5's job later in the game?

#5 General. Some players do take the role of 'shot-caller' but if the plan they laid out goes to hell, they usually end up blaming other players; Is this just a herald-phenomenon, or should I expect that type of behavior at later ranks as well?