"If the estate is sold before the citizenship, how does tax issue come into picture regarding the money account being transferred to this country?"---U r not subject to taxes to IRS on ur income generated from holding ur capital assets,i.e., stocks, bonds, or personal use goods, and personal residence in Korea
"If the estate is sold after the citizenship, how does tax issue come into picture regarding the money account being transferred to this country?"---Then as mentioned above, u as a U.S. citizen or resident alien, the rules for filing income, estate and gift tax returns and for paying estimated tax are generally the same whether u are living in the U.S. or abroad.
for further info.on income taxation issues or rules, please refer to the irs pub.593.
hopethis helps,bud~~~