We left Pingdom long ago in favor of Uptime Robot (https://uptimerobot.com/). Their free service is great and their paid service is perfect for our limited needs as a web hosting provider.

I bought into the whole "SATA is the new less-expensive SCSI" and put in two new file servers using SATA last spring. I can say that I'm unimpressed with the SATA servers as compared with our SCSI servers. I now wish we'd spent the extra $1000/server and gone with SCSI. I recommend SCSI -- you won't second guess your decision down the road.

BTW, we used 3ware controllers with WD RAID Edition HDs. We're supporting approximately 75 users per server.