Garden railway project page.
G-scale is the most popular garden railway scale. It uses 45mm track width (1:32 to European standard gauge), but rolling stock is bigger in 1:22.5 scale (G = Groß = Big).
H0-scale BR 120 DR “Taigatrommel” (small) vs. G-scale BR 131 DR “Ludmilla” (Big)
Rocrail https://wiki.rocrail.net/ is community supported free but proprietary control software for model trains.
Rocrail supports many commercial and DIY hardware. Rocrail provides many interfaces, MQTT among others https://wiki.rocrail.net/doku.php?id=rocrailini-service-en.