First off, Bruin0, excellent job making exercise an ingrained part of your life and looking for help when you feel stuck. Feeling flustered and frustrated is often caused by the same thing in workouts as it is in the rest of life: not having a plan (knowledge of starting point, a specific goal, and a methodology to bridge that gap over time.)
You have a few distinct advantages that you should leverage as much as possible, imho: you're intelligent, you're committed to improvement, you have 0 commute time to the gym, you have access to plenty of equipment
You didn't mention any injuries or mobility issues, so i'm going on that assumption.
I'll start with a quick and direct answer to your overarching question:
Deadlift, Pushup, Pullup, Handstand(pushup), KB swing. if you take that and run with it, at least you won't be doing too many exercises to get any major benefit from any particular one. level one solution- better, but not by much
now a longer answer with more meat to it:
progress through the levels of difficulty with the movements above. level 2 solution- a better idea of your starting point and that there is a goal. the road is long from here to "somewhere," though, and it's easy to get distracted by fields of poppies, crying babies, and so on.
and, finally, what I would actually do (given what little info I have about you) if I were you (level 3 solution):
Deadlift, Pushup, Pullup, Handstand(pushup) for your strength workouts
KB Ladders (deadlift, swing, clean, squat, press, snatch, first on one side then the other, from 1 rep up to 6 reps and then back down) for your cardio
all of this would be progressed in an organized and structured fashion over time (and logged for reference) according to your response to the exercises from the easiest (beginner strength) to the more challenging and heavier versions of each exercise goal strength.
you can stop reading here and run with it, or feel free to read on for my long-winded explanation of all this.
still with me? awesome.
short version of your post: i know how to do a lot of exercises and i do them, but without consistency so i'm still at a beginner level of strength despite significant time invested. limit me!
improved version: I have knowledge of a variety of movements and access to equipment. how can i get from 1 set of 10 pushups, 1 set of 5 pullups and run a 10 minute mile to 3 sets of 20 pushups, 3 sets of 10 pullups, a 7:30 mile, and feel better all the time, in 20 minutes 2-5X/week?
i'm glad you asked! the answer is right there in the two versions above. consistency (i call it "the big "C" and I always hold my hand up in a "C" in my client's face when i say it) coupled with a plan, a roadmap, elucidating that there is a starting point, a destination, and a path (20 minutes 2-5X/week) to follow to reach the destination. figure out where you are exactly, where you want to be exactly, set a time period for the goal and interpolate, basically.
you mentioned you had a hard time with a set schedule. to fix that problem, i usually simply say, for example, 4X/week instead of MWThS. That way, as long as there are 4 days left in the week I can still get it done. or, worst case, 3 days and i have to do two 20 minute workouts one day. you see the point...over a particular time period, I owe X amount of work. Using this method, I'm usually done by thursday (my week starts on Monday), giving me 3 days off of I want them. it's a sneaky trick that seems freeing but actually commits you because you can't use the excuse that you "missed Monday this week, so I guess i'll start with Wednesday's workout."
enough chatter! let me know if there's anything else I can help you with.
personal wellness coach