I am planning to install a luxury vinyl tile in my kitchen - it is a Mohawk joint and click type (see: http://www.mohawkflooring.com/flooring/luxury-vinyl-tile/) - they are ceramic tile look-alike planks - measuring 12" x 24"

As the pictures below show, I am adding a 1/4" plywood as an underlayer. I have decided to do this because the original subfloor (a 3/4 inch ply) has a lot of glue residue from the previous linoleum installation.

I have laid them out on the kitchen floor, but before I move ahead I wanted to clarify a few issues:

1. The seams between plywood joints. I want to seal them so they are tight enough. How tight should they be - Picture1 below is an example of how tight some of the seams are - are they tight enough? If not, what procedure should I use to seal them?

2. Picture2 is an example of some small spaces that are left uncovered. One prominent one is in the entrance way. Should I cover these with small plants of wood - nailed/glued down?

3. Picture3 shows a tight space between the lower cabinets and the floor. I need to nail down the plywoods there - but given tight space how do I get the nails in there ?

4. Do I need a moisture barrier for the vinyl tile

5. What else can i do to ensure a good installation - so there are not gaps between successive planks.

thanks - Oyii