Actually most of computers nowadays can afford that if running BPM Suite with default settings.
Take BPM Suite 6.1 as example,
2GB free mem. is adequate for the default JVM settings: "-Xms1303m -Xmx1303m -XX:MaxPermSize=256m",
and a default installation takes around 600MB disk space.
BPM Suite has a local repository needs some extra space, depends on the size of your project.
CPU, even old single core cpu should run it.
Sometimes I run multiple EAP / BPMS instances on my laptop.
To meet your specific performance requirements, " thousands of records to be processed in a given duration" you can start some performance testings with all default settings, then tune it according to the bottleneck you find in your testing.
If you have not a very small lightweight application the requirements is only related to the application, there is no huge overhead.
It depends on how many parallel requests you are running and what size application objects are.
There is no exact forcast possible without have a deeper understanding of the application.
Best way is to measure it.