You mention that the miner will be released 3 hours before launch. Will that be enough time to prepare a 1TB hard drive?
No. If you have a good processor, you can probably do about 100GB in 3 hours. You can run 2 instances of the miner, one for generating plots, and one for mining with plots at the same time, and it will mine with what you've prepared.
So SSD will give more number of coins than HDD ?
HDD read speeds are fast enough for this. There is no benefit to SSDs.
Would you need an os installed or can I set it to use a different drive than miner is on.
The miner runs on the Java JVM. Anything that you can run java programs on should work.
My pc has 4 hdd's, can I mine with more than one drive?
Yes. When mining, run an instance of the miner on each drive. You may want to cap the ram usage though(ex: -Xmx500m), since the JVM tends to store no longer needed stuff too long and uses up all your ram if you don't force a lower cap. The .bat/.sh scripts included in the miner will already have that flag set.