I'm not an expert, I run Start9 on a dedicated Lenovo NUC with 32GB RAM and 2TB SSD.
However, I believe the difference between Start9 and Umbrel is that Start9 is an OS, which means you will at least need a partition to run it, but if you're going to partition a machine, that means that your Start9 will not be running all the time.
That is a consideration in terms of keeping it synced to the blockchain and using it as your gateway to make payments and explore the blockchain.