So this is my first post on the forum, just looking for some advice.
I have barely used linux and would love to get into it after watching a few videos on the youtube channel
I'm a student so I don't have much money but all I plan on doing is messing around with linux to learn the basics and apart from that I will just be using it for internet browsing and maybe gaming if possible (not too bothered)
You can definitively try Linux but I would recommend using windows as your main OS and having Linux in a vm/ other contained area mostly this is for beginners because you will screw shit up if your really serious about getting into Linux. This is the way I have been doing it since I started and I recommend it to anyone who is a fan of Linux. I still use it because I screw the OS up all the time.
I really hope you do decide to go with Linux. When I started using it 6 years ago. I thought it was alien language.. But with books, and the knowledge I gain from others. I enjoy a lot.. and I mean a lot a lot.. So much I have fully committed to it with it being my main OS. If you're going to start or want to try Linux out. You can always boot from a USB Device via "Live" feature most Distros offer.
Have you got a laptop/PC already? If so, use a virtual computer to mess around with Linux. Far easier and much less messy. If you find it fun, you can dual boot and create a dedicated Linux machine alongside what you already have.
Don't have a laptop/PC? Raspberry Pi might be a cheap solution to let you enter the Linux world. One issue is that it isn't X86 (it has an ARM processor), which can cause compatibility issues with certain software (Flash is the big one not supported).
That PC might not be too bad. You will need to get a PSU and hard drive which could cost you a few quid as well. Not much but it all adds up. You may be better off looking for some shitty second hand PC for cheap.
I have the ASRock Q2900M. Similar board to yours but it sports the J1900 which is the quad-core version. Your pick will run Linux okay, Win 8.1 performs well on my machine (but I have a discrete GPU), but I think your's should not struggle too much with it.
You could also look into the QC5000 from ASRock. It comes with an AMD APU (A4-5000 or something) and wifi onboard as well as more USB (4x 3.0 2x 2.0 on the back and a 3.0 header) and 4 SATA ports. The J1800/J1900 only have two from what I've seen . It's 69 pounds and therefore nearly twice the Gigabyte one.
With that wattage you can go for a case with integrated PSU. Or you could go for a full sized PSU (that will probably be silent because it is oversized). I have the be quiet System Power 7 300W. It's quieter than a harddrive. I ran an old PSU before and once I changed to the be quiet the power draw from the wall dropped from 30 odd to 17 in idle (now it's up to 40 under load, but I have a discrete GPU).
4 Gigs of memory is enough. Lubuntu uses on my laptop 300 Megabyte in idle and Kubuntu used around 1,3 Gigabyte on the board. With Web surfing and stuff I never had any trouble in terms of RAM.
To answer your question whether it's worth building: Yes. It is. Go for it.
PS: mini-ITX is enough, the CPU only has like 2 or 4 PCIe lanes.