Excellent, can't wait for season 5. I'm elated to finally have confirmation that it is coming, and I'm pretty intrigued by the premise of the spinoff as well.
Sergei Korolev is gonna have to be one of the leads in that Star City show. In real life he died due to complications from surgery which led to the Soviet space program losing steam/fizzling out, but the showrunners have said that in the FAM universe he doesn't die and that's the main point in which the timeline splits from out own, allowing the Soviets to reach the Moon before the US. The main show never addresses this directly, but they creative team has talked about Korolev and this situation a lot in interviews and such.