How can I reduce/optimize downloads when upgrading to an SSD and installing Mountain Lion?
How much space are you using on your current drive and how big is the SSD? If your current space is less than or equal to that of the SSD, you can do a direct clone, without downloading the OS again.

You'll need to get an external enclosure (2.5" bus powered USB ones can be had for ~$20). Put your SSD in that, and you can use Disk Utility to clone your current drive to the SSD. If your current drive is bigger than your SSD (but the capacity used is still smaller), you'll have to shrink your current partition first. You'll also probably want to reinstall the recovery partition to your SSD, using Apple's tool. Once the clone is done, you can just put the SSD in your Mac and everything should work as before.

If you don't want to buy an external enclosure, you can use another external drive (if you have enough free space), and essentially perform the above procedure twice - once from the old drive to the external, then install the SSD and clone from the external to it.

The final option, if you have a Time Machine backup, is to install the Recovery Disk to the SSD (so you can boot to a recovery mode off the SSD), then restore from the Time Machine to the SSD.