Let me answer the only question you asked that I can make sense of:

using Inline::C or h2xs, following on that question, how do they compare in terms of required knowledge and free time?

In my opinion Inline::C is easier to learn and requires less time overall to use. The main advantage of h2xs is a greater body of sample code in the form of modules on CPAN. Start with the Inline::C cookbook and hit the docs when something you need to do isn't there. Also, there are chapters on h2xs and Inline::C in my book.

-sam