How would elections work under a federal system after Korean unification?

Presidential Elections under a Federal System
The president under a federal system of government on the Korean peninsula may be elected through either direct or indirect elections. A direct election would imply that every citizen on the peninsula is granted a vote carrying the same weight.
An indirect election could be carried out using a similar system to the electoral college in the US, or via a national congress or legislature. The population ratio of North and South may come into play when calculating the voting weight of either side under indirect elections. It appears likely that population numbers have a significant influence under any election scenarios. 
 
An indirect election would be the least complex, and election through a federal legislature would perhaps be the most convenient form. However, if a president is elected this way, the authority of the president may not be seen as superior to that of the legislature. While a direct election seems to be the proper way forward in the long-term, a short-term indirect system may be helpful to avoid the potential political instability that may come with a direct vote.
 
Since election through the legislature does not involve an electoral college or any other external process, it would be relatively easy to execute. It could also serve to prevent any unexpected surprises as the legislature would debate and negotiate before lawmakers cast their vote. 
 
However, the process of electing a president through the legislature comprising lawmakers from both North and South will likely be challenging. During the early period, North Korean lawmakers will lack experience with democratic systems, but can use the transition period to quickly develop their familiarity. 
 
The legislature could also become a battleground for regional and North-South conflict if a favored candidate for president does not emerge quickly. A situation could arise similar to that in South Korea during the infancy of its democracy in the 1980s and 90s, where regionalism exploded and political disagreements between the provinces became a major issue. North-South regionalism may be even worse than intra-South Korean regionalism. More research is needed to develop a process that can effectively elect a president while avoiding major regional tensions.
 
By comparison, East and West Germany did not experience regional differences as great as those on the Korean peninsula today, so political integration after German unification occurred much faster than we can expect for Korea. German Chancellor Angela Merkel’s continued popularity and time in power are a testament to the speed at which an East German-born person has been able to develop into an influential politician under the new system. 
 
But Korea is very different to Germany, and we should not expect to see a similar level of political integration within the first 30 years after unification. More detailed and meticulous research into the presidential election system is needed if Korea is to have a similar chance of success. 
 
Structure of the Legislature and Elections
 
Under a federal system, there could be a dual chamber national legislature and separate assemblies for the North and South. There is a likelihood of confusion arising though, as South Koreans would suddenly be faced with three levels of legislature. It will be necessary to clearly delineate the authority of each organ and ensure an appropriate balance of power. 
 
For example, the upper house of the national legislature could consist of 100 members, with 150-200 members in the lower house, while each North and South district assembly could also hold 150-200 seats. It might mirror the system used in the United States, where the Senate (upper house) carries more power than the House of Representatives (lower house) due to greater importance being placed on the independence of the states (provinces). 
 
The upper house could comprise an equal number of seats for both North and South, while seats in the lower house could be assigned to regions based on population. Seats in a legislature may also be assigned based on population, though the dual chamber system is much better suited to a federal system for Korea. The more powerful upper house will be essential to maintaining the independence of each North and South region. 
 
The election process could be similar to presidential elections in South Korea today, although it may also be helpful to switch to a proportional system of representation in the electoral system, which is now used in Germany.
 
The relationship between the president and the legislature could be similar to the current dynamic in either South Korea or the US. However, a semi-presidential system (consisting of both a president and prime minister) or parliamentary system may experience difficulties under a federation due to the nature of internal domestic affairs.
 
It may also be necessary to nominate a vice president or prime minister under a federal system, with a vice president being more appropriate, again mirroring the American system. But unlike in America where the vice president represents an additional 101st vote in the upper house, the elected vice president in this system should be a sitting member of the upper house so as not to influence the North-South balance of power. 
 
District legislatures for the North and South can be organized depending on whether parliamentary or presidential systems are implemented. A parliamentary system at this level seems more appropriate, although a presidential system may also work well.
 
However, a parliamentary system does offer the benefit of a stronger and faster-working legislative body. It may also be a better option for preventing the rule of a dominant minority, which has a greater chance of arising under a presidential system.