Update: I stand corrected, this coin in particular is worth ~$5 here in Korea. According to the K&C Korean Coin Catalogue we have here in Korea this is Catalogue No 18.299, coin #5 of 10. These were minted beginning in the year 1731 AD (Yeongjo Yr 7) at the Treasury Department of the Joseon Dynasty. For your referenced the first picture you have is the obverse and the second the reverse. The four characters on the reverse of your coin from the top in a clockwise fashion are the Mint Mark (Treasury Dept) > Furnace Group > Branch of Mint > Sexagenary Cycle. The last two characters can be switch out with others like the Date In or Index No of Issue, etc. The marks you are seeing all over the coin are also common with this type of coin and are not anything too special. If you have any other questions please let me know. Good find!