Alright so I FINALLY got my arsenals yesterday haha. I set everything up and it all works like a charm! I am sorry there is no best answer from other people here since I worked around on my own to figure out the problem. I will list everything down here for anyone else who ever runs into a similar issue!
My problem was: File transfer speed was pretty slow even over LAN. WLAN was also slow but I didn't pay much attention to that since wireless magic can interfere with lots of other components here and there and that 2.4 GHz frequency from other techs in the house. Same goes for 5 GHz too btw. Anyway so yeah I linked my macbook pro which has a gigabit card of course but I was not getting the speed and I checked and I was only getting close to 11.5 MBps which is what one would get if the connection is 100Mbps max.
My solution: I immediately started looking for bottlenecks! First thing was my macbook pro. It was good to go cause it already had gigabit card. Alright moving onto the next connection which is the router cause router was the middleman between the NAS and my laptop. (Connection was: NAS -> Router -> Laptop.) Saw that my router only supports 10/100 Mbps meaning 100Mbps is the max I can get. So I searched different forums for answers and people talked about the gigabit switches! Understanding how they work, I ordered one of those bad boys; TP-Link 5 port gigabit switch. Tested it (Connection was: NAS -> Router -> Switch -> Laptop). No luck!! So far, I got the following bottlenecks checked; My laptop and router. Router wasn't gigabit so ordered the switch. So far everything was good and I was down to only two more things to check for bottlenecks; the NAS itself and the cables. I bought cat 6 and hooked everything up with cat 6 and still no luck. So now I was down to my last check; the NAS itself! I looked up my NAS (PC)'s model number and found out that it's integrated ethernet card is only 10/100. BINGO! (Yes, I should have checked all of this in a single day but I had no prior knowledge about all these things such as ethernet cards that say 10/100 and all that so I played this game step by step). I ordered TP-Link 10/100/1000 PCI card for $9 off of amazon, bundled it up with 50ft cat 6 cable for $5 and hooked all that up just yesterday. Final tests showed max speed of ~77 MBps through LAN (ethernet cable) for both read and write! For those who want to know if my WLAN was improved as well; unfortunately, no. The WLAN was still spitting out only 10-12 MBps.
Oh and the last bottleneck I forgot to mention was the HDDs. But for HDDs, just know that as long as your HDDs have SATA connections, they are relatively new HDDs since SATA is the new thing and not the old ATA (wide strip of wires). Also, make sure the HDDs are 7200 RPM. I mean, I'm not sure how 5400 RPM would affect anything but as far as the proper connection goes to achieve the maximum read/write speed on whatever HDDs you have, you can refer to this guide. If there are any questions regarding this problem, you can private message me of write here. Anything you guys prefer.
Again, thank you for those who communicated with me here.