What they are looking for more than anything is to be as far away from civilisation as possible (just like mountainbikers), but with the knowledge that if they need anything, they can have access to it. That might mean that extra water, mechanical backup, etc is only a phone call away. It’s kind of impossible, but there you have it.
They want to get away from cars more than anything, so I don’t think they’d even want a support-vehicle following them all the time… they want to either “burn the miles” or “experience the climb” at their own pace. No distractions. It could be either riding within a group, with their partner, or alone.
Hence, roadies are sometimes best served by an uplift to a suitable starting point & preferably collection (at which point they’re knackered), or possibly even both (luxury!). Get them away from any dense suburbs and into scenic territory asap. Get them in the mountains on the smoothest roads that you can find with the least amount of traffic and they’ll be like pigs in proverbial mud. Remember: road bikers enjoy the ascents just as much as the descents. Personally, I do both & I enjoy ascending on a road bike, and descending on a MTB.
I have a feeling that road bikers training overseas generally like to stop and enjoy the local food & coffee rather than continually munch on the same old energy bars that they can get back home. But they want to do that AFTER the main climb, not before. At the summit is an ideal place for this… it allows them to re-group, re-fuel & add layers of clothing if need be. Preferably, they don’t carry their own jackets or even helmets (please don’t flame me for saying that), they’d get those at the top for the chilly/dangerous descent.
Like all bikers, they usually prefer loop-rides, not return-and-back ones. They want to know what they face. Is it a single 20km continuous 5% gradient? 10%? 15%? Will it be sunny? It’s a psychological challenge to tackle a mountain climb & they need to know what to wear more than anything… Are there any places to stop & get snacks? Nothing is worse than bonking on a major climb.