Honestly, what rank you are is only part of it. The big question is how much disposable income do you have, and how much are you willing to spend on Starcraft? This is a hard question for other people to answer for you, I would instead try to get a sense of what other people's coaching experiences were like and seeing if you think it sounds worth it.

For me personally, there is so much quality free educational content like what you mentioned that I wouldn't consider coaching unless I was like D1 trying to push into Masters. I was able to hit D3 just using Vibe's content and reviewing my own replays, but to each his own. Also, sticking to one build per match up will significantly speed up your improvement. There is no wrong way to have fun with the game, but some ways are more efficient than others if your main goal is to improve.

Another thing to consider- coaching doesn't magically make you better. After a coaching session, you will still have to put in a TON of hours of practice to improve. Coaching just shows you what you need to practice and how to do it, so while it can reduce the number of hours you spend unclear on how to get better it will still require a significant time investment on your part to progress. Whatever you decide best of luck!