Deskpro runs well on modest hardware, and can handle typical helpdesk loads when run from a virtual machine, or even a virtual hosting account.
At least 2GB of RAM is recommended.
If you are expecting a very busy helpdesk, the limiting factor for speed is generally the database, which can be helped by increasing the amount of RAM, using fast disks for storage (SSD), and installing Elasticsearch.
You can run all the required software on a single machine, but you may wish to have separate servers for the database and web server.
See the section on Performance Boosting for more information.