A common approach is to use lightweight forum software like MyBB or PunBB, which are known to be efficient with resources. For specifications, aim for at least 1GB RAM to comfortably run your web server, database, and forum software, especially if you anticipate future growth. Disk space isn't usually a major concern unless you expect many user attachments, so 10-20GB is often sufficient.

You could try checking recent user reviews and performance benchmarks for each one. Consider your specific needs regarding location, support, and resource allocation to see which better aligns with your requirements. Often the best choice depends heavily on your planned workload and budget.