Backpacker
Almost every male here who learnt in a Cessna 150/152 with a male instructor has flown close to max all-up as a zero-hour student. It isn't that different unless you are operating from a really short strip. I think you'll find that Headcorn and Rochester both have public-transport safety factor for operating full-weight in either aircraft, so no real problems. I was in Le Touquet today public-transport in something rather larger, there is stacks of runway! If he feels troubled by performance Lydd and Manston are not far off.
Passenger handling is a point worth considering. You are quite right that three on the first go is not a good idea, I am not sure that was the plan. An instructor could, again, give good advice - they are very used to dealing with some difficult first-time pax on trial lessons.
As for international flights - again the instructor will help in the UK end, but in Le Touquet they are well-set for inexperienced British visitors. Just make sure to file both flight plans before leaving. Easy enough to delay the return, and less to stress about.
Oh, and the rules changed a few years back so one pilot may nap briefly in the cruise even on a two-pilot crew. I knew a Captain who complained if he had a tired FO, as he could not get enough sleep himself.