Just a question before I leap into the Technical Preview.
Will installing Windows 10 overwrite my laptop's internal partition?
Will I be able to restore back to Windows 8 with the recovery partition after I install Windows 10?
No, you won't be able to use the recovery partition, because it is accessed through the boot manager on the main drive, which is overwritten by Windows 10. The recovery partition has to be able to boot, but the bootstrap that points to it through a boot manager is located on the primary system drive, which gets overwritten, hence it renders the recovery partition useless.
If you are running Windows 8.1, then you can search for "create a recovery drive", and select the setting by that name. Follow through the prompts, and it will make a bootable copy of your recovery partition onto a USB flash drive so that you can re-install later. This utility will also let you know how big the flash drive needs to be, which is dependent on the manufacturer and other specifics of your laptop.
I just finished getting my recovery USB drive done, and it took a 16GB flash drive, because my laptop came pre-installed with a bunch of extra software and junk, including a trial of MS Office.
Once you have your recovery saved to USB, you have the option to delete the recovery partition in order to free up HDD space (or SSD, whichever).