You should have a remote project processing computer for interference checking (IFC) that is separate from the computer hosting the databases. The interference checking computer can process more than one model. This computer does not need to be a high-end server, but should meet the minimum hardware requirements for a client computer. See Smart 3D Workstation Recommendations for these requirements.
There is not a specific hard drive size requirement because the interference detection service does not store information locally. However, we do recommend 8 GB of RAM for the IFC server when processing one model. When scaling up to process multiple plants, the memory requirements might increase depending on the sizes of the databases being processed.