We mostly ran all-wheel-drive diesels - mostly my Murphy's - but, we also ran a tender-drive Flying Scotsman, with four coaches, including a post-office pick-up-and-drop coach - no trouble. The only thing that gave any real trouble was a seven car Pendelino, and that seemed to struggle mostly because of the double bend before the slope started - if it was all on the slope , it seemed to just manage. It tend to derail, actually, as the traction tyres were only on one side.
It's a simple enough issue to do some testing with a few planks before you commit yourself. Better safe than sorry
Do beware of tight bends an or near the slope, though. They do add to the rolling resistance.
We did run various old engine drive steamers, mostly six-coupled, never had any real issues with them, often pulling quite fair trains.
Do have the lowest slope you can get away with and try it experimentally first - that's the best advice I can give.
Some of the older engines required a small power increase to get up, and a bit of a turn-down after they had 'summitted', to avoid them 'running away' - Murphies and other more 'modern' types didn't really have much of an issue of that sort. All being run through Gaugemaster DC controllers.
You can see the journey over the ramps with a 141 pulling three coaches here - longer trains weren't much of an issue.
The ramps are at the back, immediately after the start - either side of the suspension bridge.