Hello Kim,
I am also a newbie–well, I’ve been working on my audiobook for a number of months now, and I’ve learned an awful lot by using Audacity and especially on this forum.
There are true experts that help out on this forum, and I’m sure you’ll hear from them (e.g. Koz). But to try to get you some early answers, and maybe for me to give a little back, I’ll share some things I’ve learned. I will not be offended whatsoever when they correct any stupid things I say!
Is Audacity the right product for him?
I would say yes. It is very capable. It is free and well-supported. This forum provides good assistance.
How much space do we have on Audacity to record his book?
Ok, no. Audacity is a program (application) that runs on your PC ( or Mac). The recordings your dad makes will be stored on the PC’s storage, so on a hard disk drive or solid-state drive (SSD).
Read as many forum threads as you can about getting set up and started. Your dad’s “recording studio” and equipment are probably the most important things in the whole process. The studio needs to have as little noise as possible–no garbage trucks or trains or sirens. Turn off the A/C fans if you can hear them at all. Turn off other computers if they have fans running. If the recording PC (tower or laptop) has running fans, put it down and away and isolate the microphone from that sound. Koz and the others have successfully beat into my brain how important the original recording is. You do not want your dad to have to record his whole book a second or third time. So set up the studio and have your dad practice, and then submit a RAW unprocessed WAV file here:
https://www.kozco.com/tech/audacity/TestClip/Record_A_Clip.html
Equipment – I’ve been learning the hard way. I started using the boom microphone on my EPOS Sennheiser GSP 300 Headset. Big mistake. The mic is too close to the mouth and picks up plosives (e.g. bursts of air during “p” sounds) and sibilance (strong “esss” during “s” sounds). Also, a noise-cancelling mic is a no-no. But your dad does need a closed back headset. Listening to his recordings on speakers will not cut it for editing and mastering. So, I switched to using a Samson Q2U USB/XLR Dynamic Microphone, positioned obliquely to avoid plosives and sibilance, with good results so far. I use the USB interface to my laptop. XLR is supposedly “better”, but that requires additional hardware. My headset ($40) and mic ($70) are fairly low-end in price. But don’t rush to order–wait to hear recommendations from some others on here.
By the way, audio-only work is typically sampled at 44,100 Hz (44.1 kHz), and audio for video typically at 48,000 Hz (48 kHz). Because I am doing audio-only work, I set my mic to a sample rate of 44.1 kHz. Because otherwise the 48 kHz digital audio will eventually be resampled at 44.1 kHz, which should work fine, but why ask for trouble? (At 44.1 kHz sampling, the Nyquist frequency is about 22 kHz, which is above most human’s hearing.) In Windows 10, I right-click the Speakers icon (lower right on screen), Sounds, pick the mic, Properties, Advanced, Default Format.
Ok, back to the storage question. Audacity offers to save your work in “Audacity project” files. I don’t do that, because I’ve read on here that it’s better to go with the compatibility and safety of WAV files. If you don’t understand how audio is digitally stored, you’ll need to read up on that. Some formats are “lossless” meaning they don’t throw anything out to save storage space. Other formats are “lossy”, meaning they use less storage but throw away some things. So, for example, WAV files are lossless, and MP3 files are lossy. So you will NEVER store your dad’s original recordings in MP3 format, because every time you edit an MP3 things get worse.
When your dad finishes a section (like the preface or a chapter, or several chapters if he likes narrating in longer sessions), from Audacity you will EXPORT to a WAV file. The parameters you will use will be:
WAV, Mono, 44100 Hz, 32-bit float (always let Audacity work at 32-bit float)
Do everything in mono!
In File Explorer, you will make a directory (folder) for your dad’s audiobook. Inside that folder, you will make subdirectories. For example, you can name one “Raw WAV Files”. That is where you will point Audacity to save the raw recordings. Name each file in a smart way, like maybe “Chapter 1 Raw WAV File.wav”.
So now, finally to your question–how much space. For WAV, Mono, 44100 Hz, 32-bit float WAV files, I am seeing roughly 11 MB per minute. So in Microsoft Word (or wherever your dad’s autobiography is stored), get the total number of words (in Word, use Review, Word Count). Let’s say it’s 23,000 words. A reasonable narration rate is 155 words per minute (wpm), or 9,300 words per hour (wph). Note that this is not a GOAL, it is just a number that gets thrown around. Your dad should narrate at a speed that’s comfortable for him and the listener. So your dad’s book would take about (23,000 words)/(9,300 words/hour) = about 2.5 hours = around 150 minutes, which would take up like (150 minutes)(11 MB/min) = 1,650 MB, so less than 2 GB. That’s nothing. Then you will have other folders, like “Edited WAV Files”, “Quality Control WAV Files”, “Mastered WAV Files”, and finally “ACX-ready MP3 Files”. (Do ALL of your work in lossless WAV files; only encode to high bitrate MP3 files at the very end, before submission to ACX). KEEP ALL FILES! I doubt that all of your dad’s audiobook files will add up to more than 10 or 20 GB. So storage should not be an issue at all.
Where is the audio recording stored?
Answered above – on your computer storage drive(s).
How to back it up?
Ok, I am anal-retentive about backing up. You must do your backups to a different drive than the drive on which you are storing the original (and working) files.
This is what I do (for all my work, not just audio stuff):
a. I copy all files to an external USB hard drive. These are cheap. I have a 4 TB drive that is powered through the USB-C cable, so no other power cord.
b. I copy to a USB-3 flash drive (thumb drive). You can use a small 16 GB or something larger. I happen to use a 256 GB drive and some 64 GB drives. I carry them with me (honestly), so that I have backups that are offsite in case something happens.
c. I use a cloud backup service. You can use whatever you like. I happen to use Backblaze. This backs up all new files every night. I think it’s like 8 bucks a month.
Is this a good choice for the audio book and to be able to share it with publishers or to publish it directly on the web?
I believe so. It’s how I’m doing my audiobook.
You should know if you’re going to publish the audiobook online, you will pretty much have to go through Amazon’s Audible (and then add others). Which means submitting to ACX, which is part of Audible. So first the book needs to be already available to buy as an eBook on Amazon. And second, your final audiobook files need to meet ACX’s standards. The people on this forum can help teach you about that.
Can it be converted into other formats if necessary?
If you mean other file formats, yes, of course. But there will probably be no need.
Please also send me some resource links /preferably very simple videos to give me a brief (but thorough) tutorial about how to use Audacity for audio book recording and sharing to start.
I will let the experts recommend that best online video tutorials for you to view. You can just do a google search on “audacity training videos”, but be aware that some are old and Audacity evolves.
But for learning about the audiobook PROCESS, I highly recommend you go through the four-video series that Koz pointed me to:
You might also appreciate the discussion Koz and I have been having:
So… don’t let all of this scare you. The more you play around with it, the more sense it makes. I’m finally getting near the point of being ready to record. I only want to do that once! 
Please keep us informed!
Zash