Hang on to that stuff. Over time you will collect all sorts of items that are useful / interesting. Occasionally I (and nearly everyoneelse here) end up getting miscellaneous boxes of stuff that are thrown in with a machine, come up at auction, yard sales - you may find a use in the future, you may be able to gift it to someone getting started, you may be able to trade it for something that works for you - but don't be in a hurry to get rid of things.
How large a chuck is useful? That totally depends on the tasks at hand. I have a 15" lathe. I picked up a large ugly 14" 4 jaw - cleaned it all up, made new jaw screws (it is probably 100 years old). I don't use it very often, but it is great for those certain jobs. Granted, the "proper sizes" are the 10" 4 jaw and 8" 3 jaw, and the get used more often.
I also have a smaller lathe (11"), which has the same spindle mount (D1-4). This machine came to me needing quite a bit of tender love and care - took a couple years to get running. However the chucks were quick to clean up - so I adjusted the cam pins and for a while would mount them to the 15" lathe as needed: an 8" 4 jaw, which is a nice little half height chuck with narrow jaws that will close down small and let me hold in small bores and a 6" 3 jaw that will also close down pretty small (and get into small bores).
The point being, it is helpful to have lots of work holding options. You can definately use that drive plate as a face place (or even a drive plate).
The big drill bits? They would clean up very nicely. They cost a fortune, and you never know when you'll be able to make something of them. I had a very nasty 1-1/4" drill bit - someone had turned down the shank and welded a MT4 sleeve on, not real straight as the outer end had 0.16" runout when the drill part was held in the chuck (then it was left to rust for many years). I had it kicking around for about 30 years and finally decided to fix it (it took me that long to get a machine that could crank it!). Anyway, I straightened the shank, and recut the taper (with such a shallow taper, when you take off just a little you lose a lot of length) - it cleaned up very nicely. The runout is bang on, the taper nice and sticky. Sure it is a bit short, but for occasional use it should be fine.
