I would be tempted just to plug the SSD into the new build and see if it works. You probably want to try uninstalling as many motherboard drivers as you can before making the switch. You might need to do a repair install, or fix boot or something if the change to UEFI breaks the boot sequence. Worst case it doesn't work, and you clean install instead. So back up everything you need first.
If you do a clean install, you will probably need to reinstall any programs installed to the HDD as well. There might be a couple of exceptions, but most will have written to the registry, or your user folder, or something. But TBH I wouldn't bother to uninstall them, just reinstall over the top if they don't work, and see if it keeps any user settings.
And a secure erase will only be useful if you have been running without TRIM. So if you were upgrading from XP, then sure. But as you have been on Win 7, everything should be trimmed already. (I assume that your south bridge supports trim)
Do it agian this time, and ghost (or alternatives, any suggestions?) the ssd to the hdd as soon as you have everything as you want. Then a fresh install should be simple.
Only if you are keeping the hardware the same. Upgrade the motherboard and the image will have exactly the same problems as just booting from the same SSD.