Is there any risk that over time the entire floor with shift in one direction (towards one wall) if a 5/8 gap (to walls base plate) is left for most of the perimeter? 

1) So that in effect that side no longer has an expansion gap, and bulging could occur?

2) Or the wall side 'moved from' could develop a gap that actually shows from under the base molding (3 1/4 x 5/8" MDF)?

I have removed all the baseboards. There is plenty of space (ht. +/- 3/8") for the .56" thick Allure Grip-Strip vinyl planks to expand under the 5/8" thick sheet rock. My thought is to install the first row at the outer edge of the drywall so it can 'expand under' it or 'contact towards' the 5/8" base molding. 

My vinyl planking:  http://www.homedepot.com/p/TrafficMASTER-Allure-12...

This flooring will cover a 13' x 14 bedroom, continue into a hallway which opens to a 6'x6' vanity area, thru a doorway into the toilet/shower room. Also there are sliding mirrored doored closets off the hallway and vanity areas.  The longest run is 27' from a sliding glass door in the bedroom, down the hall, past one closet to where you enter the master bedroom.

3) I am not sure what kind of molding to use where the planking meets the vinyl slider base frame. I wonder if glueing a 3/4" shoe molding to the slider's base will hold. The only baby threshold I have seen is for MUCH thicker flooring than my 1/8"+ vinyl planks. 

4) How small of a gap should I go with at this (slider) end of a 27' run? This area gets direct sun, so I'd expect the maximum expansion in this sun exposed end of the floor. While direct morning sun is on it in mid summer, the floor will be ≈ 95ºF. The rest of the room will be ambient room temp. I figure I can start out w/ maybe a 1/4" gap at the slider itself, do not install any molding until I see what maximum expansion on a hot day looks like. I think it would be easy to trim off another 1/8"+ as needed at any time (before molding).

[sorry for the novel... ;o)