Start Stellaris in the early days of space travel, when FTL is merely theoretical & a practical drive system has yet to be concieved.
The immortal trait adds +10000000 years to you leader lifespan. The Demigod trait adds +1000 years to your leader lifespan. The Bioengineering trait adds +500 to your leader lifespan
There are a lot of mods out there that add new ships. Some I find quite good, others I find excessive (too many turrets, too much shield/armor/power).
Improved Space Battles (ISB) attempts to improve both the visuals and gameplay of ingame Stellaris’s space battles.
Have you ever wondered why all of the races in Stellaris have nearly identical military structure, form and ship technology level?