The explosive growth in the RISC-V ecosystem has brought about a multitude of open RTL SoC implementations, as well as broad software compatibility, presenting the opportunity to perform computer architecture research with direct impact using real implementations. However, putting these together in a research context with small, agile teams of developers has been challenging due to difficulty maintaining hardware compatibility with complicated software stacks, slow software RTL simulators, and poor introspection, productivity, and modeling-accuracy with FPGA prototyping. While our prior work described FireSim's capabilities as an FPGA-accelerated cycle-exact datacenter simulation platform, in this paper, we delve into the internals of FireSim and walk through a case study simulating a novel hardware accelerator (Hwacha) that shows how a researcher would use FireSim as a tool for rapidly and cycle-exactly modeling their own systems that build on a single-node RISC-V SoC. We discuss how FireSim addresses the challenges of building a reliable, reproducible, and productive RISC-V research environment, including packaging standardized releases of compatible RISC-V software and hardware, automating the process of running cycle-exact simulations on cloud FPGAs that are orders of magnitude faster than any software simulator, and providing debugging tools that allow introspection capabilities not available in FPGA prototypes.