Sounds like you're having great fun! Lovely little lathe, don't be put off if its a bit worn. as long as the headstock spindle has no lateral or longitudinal play and most older lathes can be adjusted and adjusted. I had a 55 year old tired ML7 for years. You get to know where its accurate and where not and just have fun. So the first thing to do is make yourself some bushes for the collet. I've only got about three collets because they are so expensive (they are all second hand), turned up a selection of bushes out of ali or brass. In fact, my nc mill just has one anoying metric collet and I have never got round to replacing it. Turn them to diameter and drill and ream for your cutters, then just slit them with a razor saw just over half way by hand from each end 90 degs apart, and you can use all your cutters. 2nd hand reamers are usually OK for softer metals or borrow one just for that job. Oh, if you cant already, learn to gind your own turning tools (sherline has a good pdf on that), much cheaper. Don't forget that broken files and drills are all good tool material, can be ground to the shape you want and can be mounted in mild steel bocks in the tool holder. Broken needle files make excellent small boring tools brazed into a bit of bar.

Taper drill chucks are in all sorts of sizes, popular tapers are Jacobs (JT1, JT2 etc_ and B. But they're all different. Tapers safer or just apply a little nut lock on the thread. Chucks never really run true and they wear, even if you spend a lot (drills bend anyway!). Cutters are much harder and snap, with very small cutters in a drill chuck they are really going in circles rather than rotating.

Most importantly... have fun!