Infra: I was hosted on Google Cloud for a while -- literally a single VM running Docker Compose, but I decided I wanted something a bit more flexible and interesting, so last month I switched everything over to Fly.io and I am incredibly happy with them. It's just so easy and fun to manage.
The retail site (rarity7.com) is just a small VM running a Crystal server process to handle web requests. Image hosting is all done on Cloudinary. My backend / inventory management / trading + research engine is a separate Crystal process in a separate VM. Both connect to a Fly Postgres DB. There's one other service which is a small python process on another VM which is doing inference on my regression model. That's super lightweight and I don't need any GPUs to do the inference (tabular data is nice like that).
Overall it's really nothing fancy and it works quite well. A few web-serving VMs and an inference service for my pricing model. I train/retrain the model a few times a year on a local box (my repurposed gaming rig running a 2080Ti).