I know you haven't copied mine. The inspirational picture you used is one of the best light weight bobber you can find. everything about that Bobber is just right.
Mistakes I made
Well as far as the mistakes are concerned I'am not very far ahead in the project so fortunately there isnt any mistakes yet that I can talk of. I research everything before I go into action so, I chose the CD175 for its weirdly strong frame.
Why I chose CD175 Frame
The metal used in CD175 frame is really good. But a T-bone frame comes with its own challenges. You have to work within the confinements of the frame. You cant fit a very large engine in a CD175 frame as the engine is entrapped inside the frame from 4 sides (Top, bottom, front and back).
Engine Options for CD175 Frame (Why I chose SR250)
I did some measurements, for the CD175 frame you can install, CM250 engine or an XL180 without any alterations. However I choose a SR250 engine. As its a single cylinder engine, its is a good 47 cm high. As my chassis already needed some rust repairs so I opted for the SR250, had to trim and adjust the frame from the top and bottom to compensate for the bigger engine. But is was a good move. The engine is the focal point of a bobber, an SR250 engine on CD175 frame was snug fit, there aint any gaps and it looks really cool.
Best Chassis for Bobber Project
I think if one is planning a bobber project than my advice would be to go for an Hero RF125. Its basically a clone of Suzuki GN250 and has a lot of room in the frame to handle alterations and bigger engine. Also its back end can accommodate a decent size rear tyre. I think a 120mm wide tyre will fit in easily. So as it Chinese it will become a nice and cheap platform. junaidakhtar01 chose it for a reason for his bobber project. Actually RF125 was my second choice after a CD175 frame as I really like the Tbone frame.