Heh, good luck. I've done a few calcs of my own, and the biggest problem for me right now is how long it takes to process my turns because of all the ships in the game. I'm not sure I'll have enough time to finish a full 150.
Seriously though, it doesn't look like the game restricts you to the setting for max # of ships in startup. Even if you restrict yourself to 2000 ships & bases combined, you should be able to hit 50M+ by turn 150 using the biggest space station with the first Version of the master computer and lots and lots and lots of organic armor (again Version 1) to bring the total to 1510kt.
At a cost of 6500m, 4430f, and 1000r, a huge world should be able to pop one of these out a turn. Large and medium worlds every other turn at least. If you set things up right, hitting 2000 ships is a feasible target. Now worrying about the infrastructure to support all those ships... Well, I think I'll wait until next month before mentioning that, heh.
-Drake