It sounds like your machine is set up to be self oiling, a machine without that feature would not have that much oil in it. You don't have to use that feature, you can just oil it by hand if you want to, just don't re-fill the oil reservoir.
The difference between the 225 and 226 is that I don't think the 225 has reverse, and the 225 will sew 3 1/2 to 4 stitches per inch while the 226 has a 5 stitch per inch maximum stitch size.
There's no way to determine what the loose needles are, the difference is in the thickness of the shaft so just toss them out, they are probably used anyway. For how to thread the machine look at post #4 in this thread: CLICK HERE