The Swordmage (13th Age Compatible, from Dark Pacts & Ancient Secrets)

There's some confusion in my group about the Access to Wizardry feature. The way it is worded, it is unclear whether you can replace any number of your Swordmage spells with Wizard spells that are 2 levels lower, or if you may only do so for one spell.

The Adventurer tier feat from the Academy Training talent says one may swap one spell with the Access to Wizardry feature without the 2-level penalty, but does that replace (Feat is essentially a buff to AtW, making it so the one spell you get can be level-appropriate) or add onto (Feat makes it so you can take one level-appropriate spell and one/any number of spells with the 2-level penalty) the talent? My group disagree on whether or not the feat implies the more liberal interpretation of the class feature.

Doubt…..why some spells don't have the "upper level" version? Example: "Ghost Strike" (on page 92). There is only the 3rd level version of the spell. How can I memorize it when my PG arrives at level 7 and it can only use spell-slots of levels 5 and 7?