Bike shops are asking 100+£ for a bike assemble and it might be justified but its too much for my budget and I want to DIY it.
Is that risky to do by watching youtube videos and borrowing tools from friends?
I want to install an english threaded bottom branket with a squared tappered crankset, disc brakes (mechanical), headset (threadless including cutting stem).
I’ve completely disassembled and reassembled a bike to have the frame powder-coated, and think it’s pretty easy and no big deal.
But then again, like the other guy who built hot rods etc., I’m an engineer and might be underestimating the difficulty for a normal person.
I suggest looking for a bicycle co-op where you can work on the bike yourself, but tools and volunteer assistance is available if you need it.
I second the idea of looking for a bike co-op. Or even ask at small shops if they would be interested in teaching you. I have known mechanics who would happily stay after hours to help people who wanted to learn. In either place you will have access to the right tools and a wealth of knowledge.