tile and overview

[joerg p]

hello,

I downloaded several overlapping europe etm+ mosaics, reprojected them
to geo. Each file is around 1.2 GB. For better performance I know I have
to tile them and build overviews.

To tile and remove the overlapping, i would like to first combine all
images and then to tile them.
It's gonna be a really huge file during this process, around 18 GB, does
this work?
Could someone give me an example of this gdal combine command? I can't
find it.

How many overview steps should I build, is there a rule of thumb?

thanks
joerg