There is a great advantage in any game to be able to act after someone else has been forced to act. A simple example is roshambo, or rock/paper/scissors. Let's say you get someone to agree that they have to go first and then you can make your choice. It becomes an easy game for you because whatever they choose, you can pick the right response to win every time. If they choose rock, you choose paper. They choose paper, you choose scissors.
Going last in poker isn't nearly as great an advantage as it would be in roshambo, but it is still an advantage. By going last, you get to see what everyone did before you have to make a decision. Let's say there were two limpers in front of you pre-flop and you raise 6 BB with AKo on the button. Both of them call. The flop comes Q96 double suited. You get to see what they do first. While they could be trapping, a check is more likely to mean they don't have anything. You could cbet 10 BB and have decent odds of taking the pot, netting you a nice pot. If they bet, the odds are they have a hand better than your hand. You can simply fold. You save the 10 BB you would have bet if you had to go first.
Position is one of the 4 cornerstones of winning in poker. The others are card strength, initiative and skill. Have a majority of those four elements and you are more likely than not to win the hand in no limit hold'em. Of course, they can have different weights depending of the circumstances and an overwhelming advantage in one can over come some of the others. For example, most players can win holding AA in any position even if they don't have a skill advantage.
Position doesn't have any location with such an overwhelming edge, but most players are winners on the button. So when looking at the four elements, we want to have an edge in several of the others if we have an automatic disadvantage in position. We can't do much about skill. Either we have an edge or not. We aren't going to develop it at the table during the hand. The next area is card strength. We compensate our position disadvantage with card strength. This is why most writers suggest a tight opening range in early position along with mostly raising. The ranges open up more as your position gets better. If you have a skill advantage (note that most players have a far smaller edge then they imagine), you can play more hands as well.
What hands to play is another subject. There are plenty of starting hand guides out there and as you get more experienced, you'll find that you the hand selection will vary with the table conditions.
Perhaps this is a bit of a sidetrack, but there are two red flags in your post. The first is the idea that poker can be played perfectly. There is no correct way way to play poker, as it is a dynamic game with opponents constantly adapting to you. There are a series of considerations and analysis's that can be performed to find the most correct decision in each case, but there is no 'perfect' game.
Similarly, there are no rules that should be followed 100%. Almost every question that is asked will have an answer of 'It depends', as there are no hard and fast rules.
Poker is a game of information and misinformation. If your opponent is able to figure out what you do and how you play, they will have a huge advantage. There are guidelines, for example, for starting hands in different positions. But if you use those guidelines religiously, you opponents will be able to put you on an exact range, and this will give them a great advantage.
Perfect play means that occasionally, you have to play very imperfectly to maintain some level of unpredictability. One of the key rules of poker is to not follow a set of rigid rules.
I'll admit that I only skimmed the op and responses. Here's what I think about position:
preflop decisions are dictated by the number of players yet to act, and any action that has happened in front of you. Then when you enter the pot, you're basically staking a claim in a portion of the pot, which is assumed to be a bigger portion than your investment. Then as other people enter the pot, they're also staking a claim in a portion of the pot, which is also assumed to be a bigger portion than their investments. This dynamic of betting leads to these typical situations:
blind position with a relatively wide range vs a strong ranged preflop raiser
preflop raiser vs preflop in position caller.
preflop raiser vs in position caller + a blind.
preflop raiser vs preflop 3 bettor.
etc.
The list goes on and on with possibilities of what can happen preflop, which will dictate proper postflop play. Which type of situation would you like to discuss?
