I would advise you build the track to 7-1/4"g for the passenger-trucks, with a third rail for the 5"g loco. To my knowledge no-on has had problems with the resulting, off-centre draw. You will need to ensure a raised portable-track is built up and stabilised more carefully than may be sufficient for a ground-level equivalent on the same ground.
Regarding replacing the old HSE Guidance, it was drawn up partly to avoid our miniature-railways being treated as "fairground rides", because meetings between the hobby's representative and the HSE soon established that would have mde us safe by simply rendering it basically impossible to operate at all.
I attended one such meeting, with Her Majesty's Principal Inspector of Fairgrounds (from HSE) as the speaker, and hosted by the Southampton model-engineering society. He understood our needs, and emphasised and explained the "duty of care". He told us to safety seriously, and be able to show we do, but not so we stifle our own activities. I remember him saying, "You are not building nuclear power-stations!"
I am not a lawyer and we all know the allegation that an insurance company's aim is to avoid settling claims in a logical and common-sense way; but the law's main message is, do all you sensibly can to minimise the risks, and show you are doing that.
It's also worth remembering that some people will try it on, and most such claims are indeed thrown out by insurers and solicitors as invalid – the incident was the claimant's fault or occasionally, proven to be a downright lie. I recall learning of one claim for spark damage being proven fraudulent by the club's own log-book showing the event was a battery and i.c. loco day, with no steam locos.
If you can show you "taken all reasonable care" – and I would include anti-tipping rails on raised tracks, and side-sheets to keep legs and feet outside of trucks – you will have a far better chance of withstanding claims.
If a local-authority or other body tries the "fairground" route, it should be possible to show you are following genuine legal, insurance and good-practice routes designed by people who understand the matter, and the HSE and our insurers separate our railways (and rides behind miniature traction-engines) from commercial fairgrounds.