Von Reinbek had never operated a steam locomotive, but had fond memories of days riding trains in his childhood. So he started small. Very small.
The Royal Württemberg State Railways operated a small fleet of steam-powered rail cars built by Esslingen, a formative engineering firm that lasted over a 120 years when it was finally acquired by Daimler-Benz. Woefully underpowered, they were modified by an Esslingen mechanical engineer, Eugen Kittel.
Von Reinbek had a friendship with Kittel that dated back to their days partying in Stuttgart. The Kittel and Von Reinbek families had been friendly, so they felt quite at home, particularly at the local pubs.
During one night out Kittel was lamenting the poor performance of the Esslingen rail cars. Von Reinbek off-handedly suggested he flip the boiler around. The penny dropped in Kittel's brain, and his modified vertical boiler became the hot news in steam train circles.
Von Reinbek chose a Kittel-modified rail car as his first locomotive, and so began his collection.