Im not sure if I'm correct but before Obito was revealed as being Tobi and even after so, he used Kamui A LOT
How did he not go blind or atleast come close to it?
^A lot of this, Senju DNA, etc. Plus it's also been inferred that Kamui doesn't accelerated the blindness of the eyes as fast and thus the tech isn't as harmful as say, the Amaterasu (Note a lot of what I've heard is speculation)
Senju DNA is the go-to explanation on the base, but it doesn't hold water in this case if you ask me. I chalk it up to plot, where senju DNA becomes a convenient excuse.
Im not sure if I'm correct but before Obito was revealed as being Tobi and even after so, he used Kamui A LOT
How did he not go blind or atleast come close to it?
I would say that it isnt a sharingan/mangenkyo sharingan techique that doesnt cause blindness like koto amatsukami, though he was able to spam it because of Hashirama's artificial body/cells.