Multiple I2C devices on a single port?

Is it alright to connect multiple I2C devices (i.e., accelero, gyro, magneto and pressure sensors) to one I2C Port on AT328?

Yes. They should all have different I2C addresses so you can talk to them separately. There are 127 addresses available.

Some devices let you change them from their default address so you can have more than one of the same model device on the I2C bus.

Yes, in fact that's the whole point of a bus like I2C.

There are various physical limits to the number of devices and wire lengths, but as John said.

What do you have in mind?