Yes, a 10x4 is too small. A 10x6 MAS is on the small end, but I used one for a long time on my Kaos. It absolutely screamed in the air with that prop. I use a 10x7 Scimitar now, and the plane has better straight line speed and still turns a lot of RPM in the air.

My needle valve is less than 1.5 turns out at a peak setting, so you are ok there.

Any engine that has sat long enough for the carb to seize needs new o rings all around. The needle valve o rings and the carb o rings will allow air leaks which play havoc on your tuning.