I am sure everyone has struggled a bit in the beginning. This can even truer for people who have been using other similar software and try to use Blocs in the same manner they were used to. It’s like going from Windows to Mac OS, it is a whole new world.
That said, I find the online documentation to be fairly comprehensive and have used it many times to reply to people asking for help. In my opinion, a manual would not be more helpful. The issue is more about what am I looking for, and searching “correctly”. This is also searching the online forum and eventually opening a ticket. Having details of every single setting and available options will not make you more proficient. To be more proficient, you need to learn Bootstrap basics at least.
Additionally, since Blocs 3 is based on Bootstrap 4, Bootstrap 4 documentation, tutorials, examples, etc… can be of used as well for fine-tuning. Another resource is the inspect elements in the Blocs preview which you can activate on demand and see the actual coding, classes (which you can then customise), etc…
And, of course, the videos from @Eldar (there are quite a number of free ones).
With respect to the forums too slow to respond, I note that this is only your third post since you joined in May '18 and your topics were rather general than specifically requesting help.
If I were you, I would try to use the forum more often. You would be surprised to see how many people help and assist others in a timely fashion.