This Begonia species is an excellent true miniature species. It will grow at a manageable speed, and trail + mound slowly.

Seems to grow fairly easily with moderate-low lighting, and a damp but not soaked growing media. I have mine growing in Sphagnum moss ontop of peat. Last photo is an example of a mature plant.

Root by laying across a damp substrate and keep that humidity up!

Good airflow is helpful
High humidity
Keep roots damp, not soggy
70°F to 85°F is the likely sweet spot for good growth
Low-medium light
Well drained potting media
Promix HP is my media of choice for this plant, and Sphagnum works as well.