The tournament has ended and I feel relieved. I'd like to think it was a success, as most of the children and parents were delighted.
Alongside experienced juniors (some Britsh winners, Terrafinal winners and finalists, LJCC winners, etc..) I had some newcomers to OtB chess, both young and late teens. Participant age ranged from 6 to 17, and levels from 600 to 1900 (probably real level 600-2000+). The older teens really enjoyed the experience compared to online, even when humbled by small kids, so hopefully other tournaments will keep them hooked to OtB chess.
On the downside, as I suspected (and warned parents), standard play is not ideal for the true beginners and 3-4 dropped along the way. Playing 5 minutes to wait 3 hours isn't very attractive for that skill group. I may put a minimum rating if organise another one.
You can see all results on the following 2 links (on mobile, click on the menu icon for more rankings and crosstables. Note that the crosstable is not ranked for some reason):
I was really satisfied with the Vega software, and I had the results up online in nearly real time, and instant pairings. Some minor display bugs, but overall happy with Vega and vegaresults. The cost is also quite favourable compared to UTU and swiss-manager.
Many expressed interest for another tournament, so I may be tempted in organising one towards end of June.
In hindsight, the most stressful part of organising is the bit where you don't know if you have enough participants to cover the venue costs.