Let him research and decide on itinerary, advise rather than insist.
Try and avoid arranging regular times for him to contact you , also, don't pester him to ring you rather than text. He's an adult now, having had what sounds like a small and possibly lonely upbringing, he needs to live a bit. Avoid any kind of emotional blackmail such as "I'll never sleep, I'll be crying with worry if you don't ring me every day " etc etc.
I'd also ensure that if, which is v unlikely, anything unpleasant happens, such as money stolen, food poisoning etc etc you don't react in a "i told you the world is dangerous, come home at once" way, but in a " thats awful, how are u sorting it... great, enjoy rest of your holiday" way.
And congratulations to you, it's a great experience for him to have before moving away to university.