I understand the desire to digitize what is not available from publishers in digital form. I never did that, but I do miss a few of the LPs that I was never able to find in digital form.
Definitely, a good ADC will make a difference. The other thing to look into is software designed for the purpose. That will allow you to remove some of the clicks and pops from the final result. You might want to digitize at 96/24 or 192/24.
I suggest asking about this topic on the Steve Hoffman Forums. The site is habituated by many LP lovers and many who have digital experience as well. I think you are likely to get good, solid information there.

