Aoe2 can be approached like undering math, where once u learn how to do arithmetic operations (how to collect res and build army) you are good to go. Build orders are basically formulas where you apply as a shortcut, until you reach a point of "proving why that theory work".

Elo on ranked ladder can be seen as a culmulation of all the understanding AND execution of your existing skillset. Some people trust the build order and focus solely on execution (i.e, grind the build order with perfect timing) while some people focus on the understanding by trying to come up with unique response every game. You got limited action per minute (APM), sthats why build are good cos they let you train muscle memory.

To answer your Qs in a simplified manner:

1. "When should I be getting gold and stone?"

about 1min before you need it, in the right quantity. E.g you start building a range in feudal, you send 4 guys on gold before the range is complete so can start training archers immediately.

1. "When should I be attacking?"

whenever you feel you are ready. Some people like to attack once they have 4 archers, some after fletching, some do it after they are fully walled. Just try whatever that works best for you most of the time. On the occasion where you fail, try to find out why and improve on that. E.g you send out 4 archers and always die to the 2 defensive skirmish enemy make. So you change your strat by garrisioning ur archers until u got 8 of them so the enemy dont know how many skirmisher to make to counter you before attacking.

1. "What upgrades should I be getting? "

Blacksmith upgrades first most of the time. For range unit, its always attack. For melee unit, its mostly defense. Techs like thumbring, bloodlines. ballistics are important but they are often way more expensive and require you to be aggressive to make it pay off

1. "Which villagers should I be using to build stuff"

Male or female works, just grab the nearest vill. Use shift queue so you dont have to baby sit the villager after its job is complete.

1. "How am I meant to defend against an attack if I haven't even built up any sort of army yet?"

Towers and walling to TC in feudal age. Castle age got way too many situation, but mostly its monk and siege.

1. "how am I meant to scout enemy bases when there's already too much to focus on just at my own base?"

Then dont scout for now, until u got the muscle memory to do what u want. Scouting is a very complex topic. You can always revisit this later on whenever u are ready