I don't know what you mean by accessories. When you order the rack server, you just install your hard drives, connect it to your network and plug it into the power supply. Then press the power button and let it boot up.
Use the "SynologyFinder" from the Synology homepage to find the rack server and then set it up as normal.
I bought the server because my old DS1815+ had succumbed to the Intel chip bug. I put all the hard drives from the DS1815+ into the rack server and migrated them. It is indeed praiseworthy to mention that there was not the slightest loss of data.
All the data, services, homepages that I host as well as the email server and the clouds for various people worked perfectly afterwards.