3D matchmove in Fusion - MCU - with trackers and mic stands

Love V9!

But -trying to track a SFX shot in Fusion - MCU - 35mm lens.

Got about 12 track markers (all crosses at half stop down - same hue) and 3 mic stands with red dots.

I am running a seperate pipe via a CC to max contrast etc before the Camera Tracker.

A few questions:

Is there a way to force it to track with only a few markers - it keeps saying not enough.
Is there a way to set my own trackers - I should read the manual
Any ideas about to best do this in Fusion - or do I need ot go to outside app (hopefully not..)

Thanks
Rolfe