Oh yeah, I don't think the way I went about it was necessarily the most cost effective. I bought half of them on sale one year, didn't get around to setting things up, then bought the other two a year later on another sale once I finally got my server put together. I got them before I had my current plan in place. At one point I thought about having more services in a Kubernets cluster or something, but dropped that idea
Also agree, RAID isn't a replacement for a backup. I have all my important data on my desktop and laptop with plans for a dedicated backup server in the future. RAID does give you more breathing room if things go wrong, and I decided that was worth it
I went through the same situation and noticed that modern hard drives are big enough for fitting RAID1 into nearly every homelab use case except high-res Video footage (including a bluray movie collection)
Two drives are easy to replace, easy to spare, consume less power and are quieter than 4+.
The only advantage i See in raid5/6 is on 25Tb of storage requirement within 3 years.
Also agree, RAID isn't a replacement for a backup. I have all my important data on my desktop and laptop with plans for a dedicated backup server in the future. RAID does give you more breathing room if things go wrong, and I decided that was worth it