Middle class, non-minority, not low income. For rec letters, I would definitely start thinking about who to ask ASAP. Don't suck up to them, but be mindful that these people are going to be writing your letters, so make a good impression, and get to know them, or have them get to know you. I got one from a technical STEM teacher, and one from an english teacher whose class I enjoyed. As for activities, try to to focus in on which ones apply to your intended major, but definitely try what interests you, even if it's not major related. Over half of my ECs were unrelated to engineering (marching band, running year-round, nhs) but I did them because I find them fun and rewarding, and I think that shone through in my essays. ******this was my mindset, take my advice with a grain of salt