Well, I “gave” 
you around two months. It depends on a lot of factors, such as how much time you can dedicate, your personal aptitude for (visual) coding, whether you have immediate guidance (a tutor, that is) when you get stuck or not, etc.
Yes, you do have to learn html/css/ javascript, but since you’d be using a visual tool, the learning process is not only not that frightening as it sounds but it could be also quite pleasing and addictive.
The forum can be very helpful when you are looking for the solution of a specific problem. The videos are nearly useless IMHO - they do cover a lot of topics but since they are videos and not text, you cannot go through them at your own pace.
Having a tutor at hand is very important, I dare say, especially at the beginning. This is how I started myself. I had the luck to have a friend of mine (a programmer) to guide me. (He actually convinced me to go for Webflow in the first place (the dilemma was between Webflow and WYSIWYG site builders)).
Of course it is possible to start on your own, using the forum and html/ CSS tutorials, but it might be unnecessarily difficult.
In all cases, I strongly recommend that you try following the learning flow suggested in the screenshot in my post. It is the easiest method I have come up with so far.
I do not recommend you to build a business around it for three main reasons:
- development of new features is taking far too long for Webflow. There’s plenty of essential functionalities lacking and plenty of Webflow’s UI usability glitches which are not only lingering for years, but there’s hardly any hope they’d be addressed in the coming year or two;
- pricing is poorly structured so as to be equally cost-effective for both parties (users and Webflow) and a lot of things in it contradict reason; on top of that, the way it is presented is confusing; billing is yet another nightmare. This has been the situation for all the time so far. Obviously Webflow lack competence in building their pricing and are unwilling to admit that and to listen to feedback (you can check the forum on the “pricing” search phrase to see what I mean);
- the new features introduced lately came with some glaring usability issues. Those have not been fixed to this day and may never be. I can see a trend of Webflow not only delivering innovation at a slower pace but also not at the quality seen before. It is also common to see new features come half-baked, lacking the complete range of useful functionalities.
I have the suspicion that the Webflow team are either too exhausted already or they have reached the ceiling of their competence and as a result they would be either abandoning enthusiasm about the product, letting it vegetate in mediocrity or they would sell out.