In my opinion, it's better to take all four sections because your performance can vary (albeit minutely) between the two LR sections based on the difficulty and distribution of question types and you want as full a picture of your strengths and weak…
It sounds like an addendum would be appropriate for your situation. One of my college professors advised me to write addendums structured as "X happened because... but X is not a problem anymore because..." Just make sure you give explanations, not …
Regular ones. Even if your actual administration turns out to be Flex, doing regular PrepTests will help build your stamina and give you double the opportunity to improve your Logical Reasoning performance.