Jumping straight into sketch is tempting and all the other steps look like a waste of time but I feel these steps are more like breaking down the product design into manageable modules that lead up to the final UI.
For user-flows you could try draw.io or whimsical.co (personal fav). For wireframes, maybe Balsamiq.
I really like using whimsical.co. It's a lot prettier than draw.io, and I think the connections are easier to mess with. That being said, you won't be able to export to SVG like you can with draw.io -- you can only do PNGs I believe (though you can have a transparent background, which is nice)
Not sure I have an answer for you in terms of your setup, but I just wanted to recommend Whimsical.co for stuff like this. I mapped my setup pretty thoroughly and found it super easy to use and keep things organized. I didn't go and add pictures, but you could do that too.
Thanks, I actually found them all on Google, but I was looking for the exact same tool/ kit he used, including the wireframes and stuff. I really like the design. Others, such as Overflow, doesn't provide wireframes.
For an easier learning curve, you are going to have to sacrifice features. I've found two that work very nicely with this tradeoff:
https://whimsical.co (works REALLY well for flowcharts but also does wireframes)
https://marvelapp.com (awesome DEMO mode options)