Glad you've taken an introductory critical thinking course. This isn't ad-hominem. Raising doubts of the validity of someone's statement based on inherent conflict of interest is a valid line of argument.
No, it would be a valid argument if the argument was "Marc Andreesen says this, therefore it must be true". It happens that Andreesen said these things, but I pointed that out because I wouldn't want people to think they were my insights.
You'll have to actually address the points themselves, sorry.
