I have a Janome QC6360 (or something like that lol). It presets my needleposition to 3.5. The shop I bought it from recommended I set it to 4.0 as it was closer to a scant 1/4" .

I use Shmetz size 80 universal needle. I used to use a 90 but switched to smaller size; not sure why I did, but I did. Not sure if I notice a difference either. I've tried Shmetz sharps but I get along fine with the universals.

At the moment I use a 3 ply, 50wt thread made by Cansew (Canadian company). Less expensive than 2 ply 50 Aurifil, but I agree Aurifil is wonderful to use for piecing. 2 plys makes for less bulk in the seams, and surprisingly because of the long staple Egyptian cotton, it is relatively strong.