600 GMAT Score - Help revising study plan

Hi there,

I took my first GMAT test yesterday and scored 600 (35 Q/38 V).

While not a high score, I was honestly very happy with the score as I had been performing quite poorly on my CAT practice exams:
Date Q V IR Total
7-14-2019 36 36 3.1 600
7-21-2019 37 31 4.5 570
7-28-2019 28 35 3.1 530
8-4-2019 29 34 3.8 530
9-1-2019 36 33 3.1 580
9-14-2019 33 33 7 550

I was becoming disillusioned with study and the practice exams, because I was putting in the time, understanding more concepts, but not seeing a consistent improvement in my scores. You'll see that I ended with the same score as my first practice test, so clearly I have to change what I am doing.

Here is what I did up until yesterday:
-Study Plan: I was following the Magoosh 3 month study plan with a focus in Math.
-Length of Time: I started on June 10th.
-Efforts: In the beginning, I couldn't keep up with the study schedule-- reviewing videos was taking me quite a while because concepts were quite rusty. For a while in the beginning I just watched lesson videos, taking notes and not doing practice questions. I started doing more questions + tests in July.
-Weaknesses: I was starting from a very basic place with math, as I hadn't really taken it since high school and am not in a quant heavy field. I was never bad at math, but am not recently practiced and mental math/basic concepts were very rusty. When I look at my error log, the concepts aren't just in one concentrated area--they're spread across subjects.
-Strengths: I did not really put in much study time to verbal. I read the Economist somewhat, studied some idioms and practiced the essay. I could certainly take some time to improve here and earn myself a few points, but quant is my focus.

Here are my goals:
-I'd love to at least get to a 650. Of course anywhere close to 700 would be amazing, but I want to be realistic.
-Have a decent quant score; make easy improvements to verbal
-Translate more knowledge into strategy and problem execution

Looking for input on:
-Length of time to study + hours per week - Right now I am scheduled to retake in 6 weeks, but could push that out somewhat.
-Minimum Quant Score - With a lesser quant profile, what minimum score might you aim for? I want to prove that I can handle quant in b-school.
-Study Plan - Should I focus on the basics with concentrated review? Do I need to suck it up and pay for a course? Should I keep doing what I'm doing and just recognize that I needed more time given where I was starting?

In general, I found that when I set a strict study plan aside, and delved deep into a concept, that's really when the learning became deeper and more ingrained. If I took the time after reviewing a problem I got wrong and delved into that concept, say percent increases that's when the learning stuck a bit more. But I'm not sure how to structure my time so I'm covering enough concepts + incorporating test taking strategy to execute on problems. This deep learning can take 30, 40, 60 minutes at times.

Any input would be greatly appreciated!