I have a 401, running with an SME 3009 S2 arm, and it's a very good sounding deck, the bass is especially good. Keep it.
I also own a Thorens 150, (running with stock arm) and although not as good as the 401 it is still capable of a really good musical performance (imho), they are great little decks, and do benefit from up-grading, simple things like a better/stronger plinth etc.
The Rega 250 / Thorens debate seems to roll on forever, no definitive outcome. Some say yes and some say no!
Most important, do check the spindle/bearing of the 401 for oil. The general concensus is for a 'heavy' solid plinth.
There are plenty of threads and advice for both decks here on VE and on the web. As for arms for the 401, think it's pretty much take your pick.