Great questions to ask, it's really hard being a parent of a traveling kid when you haven't done it before. My daughter went to Australia to visit my Dad, & tho she was with my uncle on the way there, she came back with only the stewardesses to accompany her. She was so exhausted from the flight, she was VERY scattered when she came back. Good thing your son's a bit older than that, but it's still possible to worry. :)
Travel low-down advising that comes from experience, was to always have an extra credit card with me. When I lived & worked in London, & if my then- 23 yr old daughter & I mapped out a plan to sightsee that went wrong, we got lost, or it just was NOT the same in person, we had a way to grab a taxi & be saved.
Getting a phone that works over there has been a repeated failure for me, salesmen would tell me it would work there & it really did not. Sometimes you're so tired in the airport that renting one, at some strange time in the morning, is not much of an option either. Last time I found a little phone store in Windsor that saved us with cheap phones, but it took us 3 days to find it. :(
I currently have a Google Fi phone, works off of wifi AND switches networks like Verizon and Sprint, as it finds them while traveling, so it keeps us connected here in rural NH now that we moved. Google Fi also says that they work in other countries, for no additional charge, even for data, same price, so I hope to prove it when I go to grad school in London in Sept now that my daughter's married. I would very much reccommend getting a phone someone *knows will work there, for sure.
If there are any clubs or groups that you, or he, belong to here, that also has members there, to definitely make that connection now. I found that Mensa in Britain allowed me access to their calendar once I proved I was a member here, & that gave me a wealth of options to meet people there. Just having some people in a MeetUp.com group at a pub, trivia night, whatever he likes, could give him lots of fun options, it almost always helps to have some local people to advise on details that you can't think of til you're there. :)
Travel videos on You Tube, including Rick Steves' channel, can be helpful. I would suggest that anything he studies about or watches on You Tube, to find it on a map, so he can learn as he goes. I'm sure he's doing his own preparations too, but connecting it to a map can be very helpful.
Become familiar with the currency before he goes. There are sites that show photos of each sized coin, they are very different than here. I had to get used to the idea of valuing my coins, because some of them were worth about $9 back then.
Also, use the web site: www.TimeAndDate.com
They have both a time zone & an international calling converter, it tells you step by step how to call internationally from wherever you are, to whatever country you want to call. Many people do not know how to navigate the international calling codes, country codes, etc. This fills in the blanks for you.
I also found it very handy to create a blog (I had family who was not on FB), so anyone with the link could watch my travels. If there was a problem signing in to Facebook because my wifi wasn't as secure as it wanted (happened often, on my last trip in 2015), then at least I could pop a message onto the blog for anyone who might worry. I also uploaded photos onto the blog, and realized it was a great photos- back- up.
Toughest part of being a traveler's parent is that things take longer than expected, you think he can call when plane lands and it takes him an hour to get online or whatever. Tell him about embassies, give him extra 2 hrs to check in than you think it'll take. Use video calls so you can SEE he's OK, parental instincts need that sometimes. And go visit him? :) Good luck!
