How does one calculate the "db" level
Take the ratio of input to output r = output voltage / input voltage
Then dBs = 20 Log(r)
I think op-amps are typically rated as "db" gain,
No they are not.
one would need to also need to center the voltage around 2.5V, and I believe there are chips to do that too.
Yes they are called op-amps.
You need x2500 gain.
In practice this is very high and difficult to achieve due to the DC offset of the op amp. This is a small DC voltage that gets amplified at the same rate as the other signals and is dependent on the actual op-amp. It is normally in the mV range and so will swamp this signal.