Do I need to get both the First Strand Synthesis Flex Module V2 and the Second Strand Synthesis Module?

No, it depends on what kind of targeted sequencing you intend to do. The modules are compatible with the QuantSeq FWD kits (Cat. No. 015, 113 – 115, 129 – 131). By getting only the QuantSeq-Flex First Strand Synthesis Module V2 (Cat. No. 166), you can generate target-specifically primed libraries during reverse transcription and use the random primed Second Strand Synthesis from QuantSeq, generating targeted RNA-Seq libraries, allowing the identification of novel fusions.
By purchasing only the QuantSeq-Flex Second Strand Synthesis Module (Cat. No. 028), you can generate oligo(dT) primed libraries during reverse transcription (using the First Strand Synthesis of QuantSeq) and target-specifically primed libraries during second strand synthesis, which means targeted 3' mRNA-Seq libraries. Please note that the second strand synthesis reaction requires annealing temperatures of >45 °C. In case you need to use lower temperatures, please contact support@lexogen.com.
Getting both the QuantSeq-Flex First and Second Strand Synthesis Modules allows you to generate targeted libraries in both reverse transcription and second strand synthesis (targeted RNA-Seq) to identify known targets.