Vinyl Square Installs

The landlord wants vinyl squares installed in a small kitchen--no other options. Existing floor looks like at least 2 maybe 3 layers of sheet vinyl. My questions are related to surface prep.

1.) Can I put luan plywood underlay on top of everything, or do I have to do some rip out before hand.

2.) Once I'm ready for luan.....
how is it secured? Screws? Which are best? What spacing? Do I have to fill the recessed screw head?
--Do I maintain a gap between sheets? How much? If there's a gap, what, if anything, do I fill it in with?

Thanks in advance