RAID 0 is for large/fast scratch disks only. Never use one for anything you want to keep.
If anything, you risk slowing down the OS because you've placed another layer in the works that will add complexity and latency. An OS or app is generally a lot of smaller library files and such, and the substantially decreased latency and access times of a SSD over a HDD are far more important than raw throughput. It's why when you see proper real-world tests SATA SSD scores aren't much different than those for NVMe.
Personal preference. I would have the mother board controller do it for me because it's built for it, but your limiting factor will be the controller running it. Most(but not all) consumer based mother boards don't have the controllers to take full advantage of the ssds your rocking. If you are doing it in the LVM or the OS, you are stealing resources away from the OS to do it. I like using the onboard cards because its abstracted from the os, and the os just doesnt care about it. Everyone needs a hobby. If this one is yours, and you have some extra pennies kicking around? Do it. In my mind, what you will learn, the process, and the knowledge gained is worth the couple of bucks you'll spend on that ssd. Just keep a safety net. Get a 2TB spinner that you back your data up over to. If your raid0 array eats it, or you goof it.. You have a gold copy of your data. You could spend thousands in a class doing that stuff with a teacher teaching you. Or.. You spend a few hundred bucks and get the same thing. Good luck, and keep it fun. =)
Echoing the common sentiment here; you won't feel a performance difference.
That said, I have two 1TB SSDs in RAID 0. I'm doing it because I want the convenience of a single volume, though, not for any performance reason. And I just store games on them, so the additional potential hit to reliability isn't a concern.
I bought 2 x 256GB Samsung 840 Pro SSD drives with the intention of RAID-0 them, but found after doing so that there was no point in doing it as there was no difference in performance at all. Boot times were identical as were all real world usage. Benchmarks that I ran obviously showed that the RAID array was "quicker". A single NVME M.2 drive of the same total capacity of a multiple drive RAID array will outperform a SATA-6GB RAID-0 SSD setup.