I started dabbling in semi-modular synths over a year ago with two Pittsburgh Lifeform SV-1 blackboxes, and later also invested in a Roland SYSTEM-1m and Arturia MiniBrute 2. In addition, before COVID-19, I started attending a local modular group meetup to learn more about the setups, modules, and workflow. Overall, I have been very impressed and excited by the experience. Softube Modular has also been helpful to gain a better understanding of modular setups. The said actions were done to help prepare me for the potential transition, but I can see the value in possibly starting with a few modules, and expanding over time.
The $5k amount is based on modules I would more than likely purchase eventually, but additional rack space will be available for future decisions. I initially planned to purchase a Pittsburgh EP-270 case, but after planning various setups on Modular Grid that decision was changed to the EP-420. Only about 65% I expected to initially fill. I could lower the cost by using all or some of the semi-modular synths I presently own, but cost is not my main concern.