The plans differ in the number of dedicated cores, the amount of memory, the disk size and the network parameters. Performance scales linearly: as the project grows you move to the next level without changing the infrastructure.
Before choosing, it is worth working out what will run on the server: websites on IIS, an MSSQL database, 1C for several users, or terminal access. The amount of memory and the type of disk you need follow directly from that.
● Windows is available from the Brachium plan upwards — the lower plans are Linux only.