Thinking of RAID'ing my dual SSD's - Windows 10

correct, you have to reformat, it's part of process when creating a RAID.
and the RAID will only be as big as the smallest drives capacity.
and you won't get any performance boost since you are using SSD's.
and you will need a hardware RAID controller, which may already be part of the motherboards software.

there's only a couple of reasons to get RAIDs.
performance - the load is shared across drives. (striping, fast but lose one and you lose all)
redundancy - data is copied across drives. (mirroring, always have a backup but slow as everything done twice)

and remember - RAID is no substitute for backups.

but these sort of exercises are usually fun.
you could use Macrium Reflect Free to take an image of the current system and save it to the HDD.
then RAID your two SSD's and use Macrium to reload the image - should work in theory, although I've never tried it.

Thread closed due to lack of any feedback from the OP.