The brands of blades are interchangeable except for the Martelli. Get the multi packs, on sale. If you are sawing on your fabric like a carpenter on a board, you are overdue for a blade change. The different sizes are for different things, but for most you will find that the 60 mm works just about everywhere. That is the size I use the most.
I buy the hand needles in multi packs. I know there are better needles available, but I mostly do machine work, and these types of needles are what I started using when I was doing fine embroidery at 12. That way you will have a needle on hand for almost any job that comes up.
These are NOT dumb questions! Just good ones. IF you come up with a dumb one, let me know!
I went and checked, I have the 45 mm, not the 60 mm rotary cutter, sorry.