Even with the missing accessories you are set up for a bit of test sewing. I think the stitch plate raises, so you don't need a cover plate for the feed dog. Generally both plastic and metal bobbins should work, but most seem to prefer metal class 66 (plastic version is called Apollo). I never went for snap on feet my self and don't know how interchangeable they are. I guess the slant snap on adapter might work with various sets of feet, but the one SewClassic has is made for Singer feet, not all generic sets will fit. Singer tend to be exactly the same as brands and sets for some others will likely be compatible. Westalee has a slant ruler foot for free motion, most things by far are available for the slant shanks. I would keep an eye out on ebay for a set of accessories for a 401, they turn up now and then. People like Helen Howes in the UK has a lot of vintage feet and accessories available too.
You are spot on with the grease and oil you have chosen, the smoothness of teflon is noticeable on my machines, even if it's a bit more expensive.
On my list I would have a walking foot, zipper foot, feller foot, free motion / darning foot, straight stitch plate, buttonhole foot and overcast foot. For the 401, the needle clamp for double needles can be nice too. I guess it depends on what you do and the feet you like to use. The 401 is a sturdy machine and will handle most challenges like flat felled seams on jeans and corduroy. The Featherweight is smaller and not as sturdy as the full size straight stitchers or the 401, but it's surpisingly capable. I would use it for anything in general, but pay attention to how the machine runs; when you get familiar with a machine you know when a machines is pushed towards it's limits. Most of the time it should run fairly easily.
Last edited by Mickey2; 08-05-2018 at 03:06 PM.