to use usb for baremetal is not supported and if you mangle the config files in a way doing it you will loose that on bigger updates giving serious headaches and loss of convenience
you can have two sata drives, one in the m.2 and 2nd in mSATA slot (or soldered manually if its missing)
https://www.parkytowers.me.uk/thin/hp/t620/
https://www.parkytowers.me.uk/thin/hp/t620/mods.shtml
if msata is present and you want o use a normal sata connector for a 2.5" hdd/ssd
https://www.startech.com/en-us/hdd/msat2sat3
https://www.sybausa.com/index.php?route=product/product&path=64_181_184&product_id=888
the sata part of the m.2 slot can be used with this
https://www.sybausa.com/index.php?route=product/product&path=64_181_184&product_id=889
there are also minipcie sata controllers to replace the wifi card
https://www.sybausa.com/index.php?route=product/category&path=64_181_183
and m.2 pcie controllers
https://www.sybausa.com/index.php?route=product/product&path=64_181_184&product_id=1070
https://www.sybausa.com/index.php?route=product/product&path=64_181_184&product_id=1044
https://www.sybausa.com/index.php?route=product/product&path=64_181_184&product_id=969
ps: and as you seem new to xpenology, sata multiplexer are not supported so using a enclosure with that tech also does not work