Understanding that budget is a strong consideration and sometimes, we just can't get what we want. But as these choices have long term implications, some of which may cost more in the long run, consider the following before pulling the trigger.
1. As too that 2nd Monitor... Ryzen kinda puts the kabash on that as it doesn't support IGP and you don't want that 2nd monitor stealing performance away from the dedicated GFX card.
2. Ryzen does many things well and their are many usage niches that make it a solid choice ... a build which is targeted at gaming is not one of them:
https://www.techpowerup.com/reviews/AMD/Ryzen_5_1600/21.html
Gaming frame rates lower than competing Intel chips
Higher power draw than Intel CPUs
Memory frequency options and memory compatibility limited
Setup complicated (memory, HPET, CCX, SMT, and power profile)
Boost frequency significantly lower than on Ryzen 5 1600X
Requires optimized apps of which there are not many
Lacks integrated graphics
In TPUs 16 AAA Game test suite, the 1600 was behind by 15%
Game Ryzen 1600 7600k
BF1 / 173.80 / 222.10
Civilization VI / 79.50 / 57.30
DeusEx Mankind Divided / 96.60 / 123.60
Dishonored 2 / 86.90 / 97.50
Doom / 195.40 / 197.60
Fallout 4 / 62.30 / 82.50
Far Cry Primal / 95.80 / 128.00
Hitman / 79.90 / 95.70
Resident Evil 7 / 269.30 / 273.20
RotR / 122.70 / 204.00
Sniper Elite 4 / 151.30 / 182.60
Styx: Shards of Darkness / 210.30 / 233.60
Total War: Warhammer / 68.10 / 87.80
Watch Dogs 2 / 101.70 / 86.70
Witcher 3 / 129.00 / 139.30
TOTAL / 1922.60 / 2211.50
3. The low cost of some AMD4 MoBos is obviously a significant reason to swing to this platform. But to do so w/o recognizing that there are other factors involved here would be a mistake. The way that they get the price down on these low cost boards is to cut component quality across the board. This may not matter to your son, but those who play 1st person shooter games will want "gamer standard" LAN subsystems, this board does not provide that with Realtek 8111GR.
Most gamers what a certain standard of realistic gaming audio, including the ability to discern where the sniper is by being able to "hear" where the shot came from. The audio subsystem that gamers all want today is the current generation ALC1220. This Sroick board has last generation's extreme low budget solution (Realtek ALC887). Again, realizing that getting all that may add 30 GBP to the cost .... but adding it down the road costs much more than that. AM4 and Z270 boards with equal features have equal cost.
4. Ya have about £88 in storage ... 120 GB is way too small for a boot drive, you will be cleaning it out to make space within 6 months. With the budget constraints, I would suggest abandoning the SSD for now, losing the slow 1 TB HD and spending slightly less money on a SSHD at twice the size. The SSD could be added as a Xmas present.
https://uk.pcpartpicker.com/product/NpBrxr/seagate-firecuda-2tb-35-7200rpm-hybrid-internal-hard-drive-st2000dx002
My son did this when his SSD failed recently ... he bought an SSHD and though he has the cash to get the SSD he hasn't bothered to do so ... why ?
SSD Boots in 15.6 seconds
SSHD boots in 16.5 seconds
He did put it on his XMas list tho
More importantly none of the games are going to fit on the SSD so gaming will see zero benefit from having it. All you will see out of this purchase is faster Windows Boot times ... < 1 second faster. You can compare speeds of the SSHD versus the WD hard drive here:
http://www.tomshardware.com/charts/hdd-charts-2013/-17-PCMark-7-Gaming,2915.html
Seagate 2 TB SSHD - 9.76 MB/s
WD Black = 6.34
WD Bue = 4.01
5. Yes, Id take the 1060 over any current AMD offering. From the 1060 on up, AMD doesn't really have a horse in the race. Below that AMD has the market to itself with winners across the board
6. Ya can shave a few pounds off the PSU price
https://uk.pcpartpicker.com/product/nB3RsY/seasonic-power-supply-s12ii620bronze
7. I'd drop the WiFi and run a cable but will keep it in for comparison purposes.
8/.. The DDR4-3000 RAM selected
does not appear to be supported by the MoBo .... perhaps there's been a BIOS update
Ryzen series CPUs support DDR4 3200+(OC)/ 2933(OC)/ 2667/ 2400/ 2133
7th Gen A-Series APUs support DDR4 2400/ 2133
Again, this will be a project for you and your son to do together and you will find it an invaluable experiences ... my 3 boys were all "helping" with their builds while under 10 and doing their own by 12 when they "let me help"
For the build below, you will spend an extra 73 GBP. Whether that is feasible only you can decide. I can tell you this tho ...
1. It will be faster outta the gate ... higher fps and faster game loading speeds
2. That gap will widen once you two decide to undertake overclocking
3. It will be slightly larger but quieter and easy to work on
4. In addition to higher gaming fps, they will load faster from th SSD 50 - 100% faster
5. You won't be tearing ya hair out every time you get that "running outta room on the C:\ drive" message. I still have Pcs coming bin w/ "make room on my SSD requests".
6. Game sound will be much better
7. LAN speeds will be much better ... well after ya give up on WiFi and use a cable for the extra performance
8. You have way more upgrade options, fast USB ports, etc etc etc.
9. You will lose 0.9 seconds in Windows boot time, I doubt anyone will notice
Again, hate to just tell ya change everything ... but as your son's 1st PC, these are things ya should think about before undertaking this journey. I remember being there with my 3 boys ... w"well we could get a faster GFX card but you'd have to do some chores" .. when they got older, they were doing chores all around the neighborhood to fund their next build.