So, the Sample rate for CD is 44.1 Khz. DVD or audio for film is 48Khz.
(you can set this up per project in the File > Project settings > Audio...)
As you are recording spoken word, then recording without the metronome (click) is a better idea.
You don't need to adjust the tempo of the project as there will be no need to.
If you intend on recording one file for 3.5 hours... then choose CAF. But am I right in thinking you'll be recording in bite sized article sizes per file. (I think this is a better idea).
You can record multiple audio files into one project.
When you are happy with the recordings you have made then simply use the File > Bounce function to 'render' them with any effects to a single audio file. This is where you can then convert the file to the specified medium of delivery. The comapny should tell you what format they need (mp3, apple lossless, aiff, wav, etc).
Using the internal mic on your Mac is not a great idea. It is good for non-professional applications. I would definitely recommend purchasing a good quality audio interface and a condenser microphone.
What you choose to but will depend on your budget and the quality of recording you are looking for.
Other considerations when recording are the room. An echoy room can cause issues for example, so a small but comfortable space without echo is a good idea.
Hope that helps