Yes, that H81M-E only has a PCIe 2.0 version. However, PCIe 3.0 GPU's are backward compatible with that slot. There would be no noticeable decrease in performance using a PCIe 3.0 bus on a PCIe 2.0 slot. I will be more concerned with the H81 chipset of your motherboard, whether it was manufactured before or after that i5-4460 (Haswell-Refresh) you will get. If the motherboard was made earlier before the release of the CPU, chances are, you would need to perform a BIOS update for your 4460 to work (this means getting/borrowing another old LGA1150 CPU to run the motherboard first). But there's also a chance the CPU would work out of the box. To avoid this possible issues, might as well get an H97 chip motherboard.
Based on your limited parts choices, I assume you are going to use this build for gaming. An 8GB RAM would suffice as you probably won't need more than that in a very long time (unless you'll be into serious multitasking). I would suggest getting a 2x4GB to pair the 2 sticks (as the motherboard supports dual memory architecture).
For the GPU, the 4GB version of the R9 380 would be better (if your budget permits).
For the PSU, you might want to rethink the Corsair VS Series (as well as the CX and other series). They are known to be low-quality PSU's with poorly-chosen components which have issues in reliability and safety. Choose a better but affordable PSU such as Seasonic S12II-620 or M12II-620 or G550, XFX TS Series, Antec HCG or TPG Series, or EVGA SuperNova G2 Series.