And to note, with additional filtration, close to 1 lb a gallon is sufficient.
I'm an aesthetics guy, so I struck a balance with my
lr, got it at 1lb a gallon (well...a little more, I got a nice deco piece for the top shelf).
It's all about places for the bacteria to call home, if you arn't going
lr only, you can balance it out with other filtration.
As pkremer said, there's gonna be die off.. and when you add more in the future there is the potential for a mini/major cycle event.
Best to get it all at once if possible, or live with the wait associated with spacing it out.
(and trust me, I spread it out, there will still be interesting things here and there popping up, if you are patient and observent)