Just my two cents:
I think you are on the right track by doing subassemblies. Following the flow of kit instructions can get a person into trouble. Or at least, make things difficult later. The instructions do not always consider best method for painting. I often view building a model like a chess game. You have to look several moves into the future trying to anticipate what the opponents (The model kits) next move is.
It's funny because I was just doing that last night on my current project. I was dry fitting pieces together to anticipate what I should paint first, before gluing. And I tell ya-- I need to study it more because one thing affects another well into 6 or more steps. All this goes out the window if a person just wants to build it and not worry too much. It's up to the builder.
I agree with others too that you should leave the parts on the sprue until you need them. I learned that the hard way. More than once and early on in my model building I cut the parts off only to find out that darn it--what part is what. Like another poster noted, sometimes there are similar parts, mirrored parts, and there is no way to tell which is the left or right because the instructions only give you a number. Also noted, the risk of losing parts increases greatly. I usually only remove parts for the subassembly I am working on, and not doing so before making sure there are no concerns of what part is what. And then-- I store those parts in a sealable container to reduce the risk of losing them.
I have to say that I understand the OPs drive to finish the model faster. He has a short window to finish the kit to his liking, and he wants to get it done because just maybe, school will consume him, and he won't have the time or interest later. If he gets it done over the summer, he can at least look back and say, Yeah! That is cool! I accomplished that! I am wired the same way.
My job consumes me. It is deadline after endless deadline that many I can't meet. By the end of the day, I am in no mood to build, or I don't have the time. And those daily deadlines train a person to optimize their time to get things done fast to get the end result needed. School is no different. So, I totally get the OPs urgency. The problem though, depending on what you want out of the build, it is not a fast endeavor. I must constantly remind myself that this is not a race. That internal wiring to accomplish it fast is always gnawing at me.
It's an internal struggle I face with every build. I will be interested to know how my drive changes once when I retire. Will I slow that expectation when I have tons more time? I really hope so.
Whatever you do--keep building, and try to have fun doing it!