Speeds with Optical Drive swap for HDD

My Plan:

Take my Early-2009 iMac 24" 2.93Ghz 1TB HDD and swap it out with an SSD (at least 480GB) so that I am booting from a flash drive.

My Wish:

Remove the optical drive and replace it with the original 1TB HDD as a 2nd internal drive

My Concern:

• Will that work? Does the original HDD fit?
• Let's say it does fit, are the write speeds fast enough to justify not just popping the HDD into an exclosure for use as an external USB (2.0) drive?
• IF the optical connector's write speeds ARE up to snuff, would I be better off installing the SSD there and using at as my boot drive?

Hope this all made sense.

Thanks in advance!