Glad to hear it worked!
Yes, the current code would take about 1 second to update each sensor reading.
Answers to your questions:
1. You could omit this, but why do it? If you don't have space for it on you LCD etc... then just don't display it.
2. No, we would need to add an additional step to write a change to the scratchpad on the sensor. By default the DS18B20 is configured for 12 bits. The 9 bytes are the complete response from the sensor, which includes ID#, checksums etc... If you only need .25C resolution I can probably write the code to flip the resolution bits in the scratchpad to 10bit, which would drop the convert time down to 200ms.
The resolution of the temperature sensor is user-configurable to 9, 10, 11, or 12 bits, corresponding to increments of 0.5°C, 0.25°C, 0.125°C, and 0.0625°C, respectively. The default resolution at power-up is 12-bit.
3. I have some existing code to convert C to F in one of my other projects if you get stuck on that. Also you could look in the DallasTemperature.cpp library file, since I think I saw it doing conversions in there as well. Unfortunately you will really need to do the folding, spindling and mutating to convert the data returned by the sensor to something you can read. I would setup 5 variables for your sensors then update them for each individual sensor read. On the main loop I would have an update LCD function that updated the LCD with the 5 variables each time.
You should upload a photo of the fish tank/display etc... when you get it running. Sounds like a cool project.