No, this is not micro-management, however I can see how the situation can be confusing to you. After all, you're simply trying to help.
The problem is that the resources (your co-workers) that are probably best fit to handle certain problems or projects are already being utilized and your manager doesn't want to disrupt the flow of the projects already in progress.
After all, even if your co-workers were to find something for you to do that's completely unrelated to what they're doing, it's not theirs to decide how your time is spent so if you receive tasks from them they're in one way or another managing you, causing a certain conflict of roles, also it disrupts timelines of up-coming projects that you may have been supposed to handle in the near future.
Managers are busy people and often have a full schedule of meetings, so the best way to be in contact with them in a way that respects their time and gives you the best chance of receiving feedback from him is to give him updates via email on your work-load. When you realize that you're about to run out of work you should email your manager and say that you expect to complete task X and Y in Z days and ask what you should work on next.
If you find yourself completely out of tasks, notify your manager via email and say that you're out of work and need something new to work on. You should use the time until you get a response wisely to learn something that will help you in your work and career path. Using idle time to sharpen your skills, i.e. reading articles, watching tutorials, etc, is perfectly acceptable as it makes you more valuable, instead of doing something that may not be urgent at all or useful to you in terms of experience. Tell your manager that you'll be using the time until he replies to study D but you're looking forward to more work. You can state your interest in working on a specific project that you have in mind as a suggestion if there's nothing urgent on the backlog, but don't push it.
Concerning some of your other questions, don't take it too personally if your opinions on certain matters don't always make it to the top as you're still learning the ropes and people with more experience than you probably have a better idea on certain topics, that doesn't mean that your input is being ignored. Just continue growing and your input will be more valuable with time.
Then there are the critical feedback points, I think your manager wants to find some topics that you can work on as milestones for the next review after this one. It's common for a manager and an employee to find 1-3 topics, tasks or milestones, that the employee should meet so your performance can somewhat be measured. I think the approach he's using to finding these aspects that you need to work on quite inefficient and awkward but I don't see any other reasonable reasons for this.
Until you can recognize a deeper pattern, don't worry to much about it or think that you're being targeted for doing something wrong. However, I don't quite understand about your situation with the sick days so you'd need to elaborate before making a comment on that.