are you installing from pendrive or old school DVDs?

just remove old HDD, plug in SSD, run the laptop, select boot device as pendrive/DVD, then its pretty much straightforward already

as for the windows to motherboard, youre still using the same motherboard, i dont see an issue unless youre reusing old key for new PC

the better way to install os is to use usb drive. it's much faster, and is usually error-free.

first of all, run slmgr /dlv in admin command prompt, it will tell you which version of w8 the laptop is running on. the common ones are windows core, or single language. the laptop should run in uefi mode (gpt disk type). for new ssd, you just let the windows install media to do the job for you (make the ssd a gpt disk, and populate the appropriate partitions for uefi install). the key step to install windows in uefi mode is to use fat32-formatted usb drive, and extract the contents of downloaded w8 iso (the correct version based on the results of slmgr), and use the usb drive to install the os. (alternatively you can use marfccy's way to do it too) when you boot, select uefi type of your usb drive. (it will be labelled as something like 'uefi: <usb.drive.name>' in the boot media selection menu) by default, as long as you are using the right windows version, the key in bios will be used automatically during the installation.

as for cd key, machines that come with w8 or above don't have stickers under the laptop or inside the battery compartment anymore. it's embedded in the bios. you can use belarc advisor or rweverything to view it. (for backup purposes) if somehow you cannot activate the windows with this key, you can call microsoft for help. (did this before)
no, there is no need to prep imo. you can actually format the usb drive with fat32 (for uefi mode installation; or ntfs for bios mode installation), then extract the contents of w8 iso into the drive. the structure since w8 can boot in uefi or bios mode depending on the type of filesystem format. for w7, you can do the same but an additional firmware file must be put in the right directory structure to make it work.

why you choose Crucial? This is quite pricey ...