I would like to know whether my rega rp1 turntable, which has a hard wired rca red and white output, will connect to either an era 100 or 300? 
 

can I just buy an rca to 3.5mm jack adapter and also the jack to usb c adapter?

also, I do have a pre amp and also amp, could they be connected as well or is that pointless? Very much in the dark as you might guess!

any help appreciated!