What will determine the end QL of the yalm is your Computer Literature. To make a ql300 (which is the one with the lowest vehicle air requirement), you will need 1500 CL. Anything below that will give you a lower ql yalm, which will mean lower stats and higher VA. But you'll need at least 750 Computer Literature to make lowest ql awailable. Ql of Yalmaha XL - 29478 you use, doesn't matter, so in order to save some credits, it pays out to camp shop terminals for lowest version.
The upgrade does not come cheap. It will sell for about 50m. If you're starting to get close to the 1500 CL mark, it will lower the price to about 46 mil.