I’ve read a lot about MBTI and Ni and Si I just feel like I’m not completely understanding it...
Thanks for bringing this up in the first place so we can sort things out.
Ni is like looking beyond concrete, tangible information, what you can see, hear, touch, smell and being aware of other 'qualities' of those information like a pattern of a function, certain possibilities of an event, an underlying motive of a series of acts, an impression of an event, etc. That's Ni solely. When including in the type INFJ it is most often used to being aware of underlying motives of series of acts because we are really really people orientated.
Si is like a huge internal data store. You notice everything: instead of an impression of an event, the exact acts of people (where you've gone, when, who said what, etc.), instead of motives you see only acts but you have an ability to connect these things and make conclusions if you see, hear, or touch something you have seen or touched before. You have proper ideals of things like 'a chair has four legs', and again you have this vast and good memory so that you can live in the 'here and now' in the real world. As an ISFJ you are capable of giving concrete and direct counsel to people whereas an INFJ you are thinking in theories and more like initiate - incept - thoughts in one's head.
This has just been bothering me so much lately and I feel like I need someone else’s input instead of just thinking about it for hours on end on my own.
That was the exact reason of me coming here a couple of days ago as well.
Sounds like an IxFJ to me. Yearning for knowledge and competition is what tend to drift you to IxTJ but my impression is that you are mainly people-orientated. It's always useful in our world to understand and use Thinking as well so you're fine.
Again this question is really 'transparent'. It asks for what preference you are comfortable to decide upon: Thinking or Feeling? Using pros and cons in a logic way is more like Thinking but base them upon personal, partial observations and they are not. Incorporating the feelings of others is certainly the latter as is the need to do no harm to others.
Although your preference to stay open to a lot of information could be a sign of a P. Of course just in case you are showing it outwardly - if you are organized outwardly you are most likely a J. Though your messy room doesn't sound like this. Again it could be even more deceptive in case of types whose dominant function is a perceiving function like Ni or Si. They stay open to new infos for longer naturally.
Consider the opportunity that you are a P. I and F I'm almost sure about by 9) but not about S/N and J/P.
As for 7) again I need more information: like I wrote in the beginning when you recall these memories do you invoke the details of these moments or the overall impression and state of mind you felt? It's really important.
The strongest moment when I felt like I could have written these words.

This is again a Sensing-Intuition question. Feeling at ease with theories, connections and possibilites is N, and using hands-on, empirial approach is S. Judging by 10) you are definitely an N.
6) and 11) also support it - exceptionally 11). Having a good amount of faith in your beliefs and not easily letting them go.
When I’m feeling particularly stressed I’m more likely to be impulsive.
That's not a problem regarding your preference. When under a great amount of stress types often invoke their least function from the subconscious - Se if you are an INFJ as I believe you are. Or reverting to their opposite - ESTP in your case, the 'James Bond-type'. Both encourage impulsive 'act first, ask later' behavior. You still prefer thinking before speaking in a 'normal' stress-free situation.
See 15) as well.
Again these are my words, shame on you.

Joking.
One point of interest though: preferring a 'quiet night at home' should not be confronted with people-oriented behavior. You like (a) one-on-ones, and (b) deeper conversations - two things you probably won't get in a party. You'll only get 'small talk' and superficiality - until stepping onto the dancefloor at least. There you can get overwhelmed by other peoples motives - mostly intimate ones, they are so clear.
I dislike it when people are so emotional that they can’t get anything done. I don’t like when people are so insensitive they don’t respect people.
Usually it's one way or the other.

People either can't stand too emotional or too insensitive people. I get *what* you can't stand in them and I'm inclined to think you prefer insensitive people less. Correct me if I'm wrong.
17) is your Thinking preference in work. I'm not surprised to see it developed so well after reading the first few paragraphs.
19)... I could very well relate to me again, but now it's about you. It's just clarifying what I came to know during the most part of the questionnaire. You are most certainly an INFJ. I am a lot more assured about you being N than say for example you being a J. Seriously consider and read a lot about INFPs.
And most important I'm really sorry about the background stuff. In fact and telling you the truth I'm most surprised by the impression you gave me. Being a really conscious, emotionally aware person who seems to have immense inner power to overcome difficulties.
Comment on this whole freely if you want to I only be able to answer tomorrow I really need some rest.
At last but not least there's a real chance I misunderstood some parts so I'm sorry for that. I hope I could help. Bye.