AP scores come in July. Academic year doesn't start until mid-August. The scores will make it to USNA in time to meet with an academic adviser and plan the academic year. AP scores matter.
If you can score a 4 or a 5 on an AP test, you can expect to pass the validation exam. They're easier than the AP tests (a lot less of a time crunch, no free response questions for the calc/chem exams, and very little writing for the English exam). The Chem, Physics, English, and Calc validation exams were definitely much easier than the AP tests.
Language tests will also be administered for all languages offered at USNA (more than the ones listed on the validation page). Maximum validation credit is four semesters of any language, but you may be placed in a higher level. For example, a native speaker might validate to 400 level Spanish, but will only receive credit for 101, 102, 201, 202 on the matrix. The 300 level is just skipped.
I've never taken an AP test for my language, but I can say the language validation exams are significantly more challenging than the SAT language tests and passing will put you around 1+ or 2 level on the DLPT. Doing very well and validating to 400 level will put you at about a 3 on the DLPT. To put that in perspective, that is the level of proficiency expected of military linguists and Foreign Area Officers, who are learn and maintain language proficiency as part of their profession. Language validation is geared towards those who are heritage speakers or have acquired high proficiency through four or more years of study; don't expect to pass with two years of high school classes under your belt.