For the typical RAID that is easier to install all the drives first, but Synology SHR RAID and drive/volume manager makes it very easy to expand or reconfigure RAID, although it may take a long time (many hours).
If you value your data, don't use RAID0. Go straight with SHR, which will be RAID1 (Mirror) for two disks and later changed to RAID5 for 3+ disks automatically. Performance on N54L will be more than enough with SHR (RAID5) to fully saturate your 1Gb links.
As things are now, I only use the NAS for media server for clients all over the house. My point is, that if one of the disks break down, I can just replace it, and it's not the end of the world, as I can just download the media again. That being said, everyone recommends not using RAID0, even though I can't use 100% of the diskspace. Is the performance difference drastic in any way, and how much space would the SHR take up off 4x 3 TB RED's.