[Freesurfer] Some methodological questions

I have some methodological doubts and I think somebody can give a hint.

1) I have read the paper from Neuroimage 2006 comparing Scanner, Field Strength, etc in thickness measurements. Is it possible to assume that we can mix in our study group images that come from different MRI Scanners?

2) We have some very high resolution histological data of full brain and correspondent MRI images also acquired post-mortem. Is it possible to use histological data in FreeSurfer or just SPGR?

3) Does slice thickness affect group studies. I mean we have some subjects with slice thickness 0.6mm and other with 0.8mm.

Thanks in advance,

Pedro Paulo Oliveira Jr.