1. First of all, and this is IMPORTANT. DO NOT FORMAT or modify your current boot drive in any way - the 500 GB SSD - UNTIL you've finally created a bootable, completely functional OS on your new SSD.
2. It appears that your objective is to install the same OS (Win 7) currently on your 500 GB SSD on your new SSD. If that is the case have you considered simply cloning the contents of your current boot drive to the new SSD? That assumes, of course, that you're completely satisfied with the system as it now resides on the old SSD, i.e., it boots and functions without any problems. If that is not the case, forget about a disk-cloning undertaking.
3. On the other hand you may be interested only in fresh-installing the Win 7 OS on your new SSD. That's fine, as well. The choice is yours of course.
4. If & when the time comes that you're thinking about formatting the old SSD my advice would be to do just that, i.e., perform a simple formatting operation. There is no need to perform a Secure Erase operation on the SSD unless you have specific reasons for doing so, e.g., for troubleshooting purposes when there's some indication the SSD needs a "resetting" of sorts. This is an extremely rare situation.