there was a special visa type arrangement for Singaporeans who wish to stay longer in Thailand , Thai Embassy in Sg has removed this type of visa from their website
you need power of attorney from LL to be able to register yourself at immigration.
It could be done online though, LL or authorized person with all the documents need to create the online account first uploading all the documents (owner id/ chanot etc etc ). It could be done using this link (you could check users guide there first as well)
also for Embassy in Seoul - as short term visitor of South Korea you are allowed to apply via e-visa only for tourist visa. Any long term application incl DTV required alien registration card copy submission- means you should be legal resident there during whole process and for DTV they declare up to 4 weeks for approval…