I have the Janome 3160, 6600, and the 15000. I use all kinds of thread, (even serger thread in a pinch) and have had no issues whatsoever. I use everything from top of the line thread like Aurofil to basic coats and clark dual duty it all depends on what I am making and the color I need. You should choose your thread based on what you are stitching. Here is a link that tells you almost all you would want to know about thread:
https://www.taunton.com/promotions/p...Essentials.pdf
Janome machines are workhorses and from my experience and that of my friends who own one, it takes a lot to mess them up. As for needles I generally use Organ but have used Schmetz. I buy in bulk and change them often. Again the size of needle is also based on what you are sewing.
Enjoy your machine!