2300 a month for the most part should be pretty decent. But of course it depends on what you want for your lifestyle.
I assume you don't want to stay in a goshiwon or anything like that, decent one bedroom apartments go from around 450-800 a month or so, depending on neighborhood and size.
The bigger issue will be deposits which are around 3000-7000 dollars which you have to pay all at once, though if you use airbnb you'll have to pay more in rent but probably won't need a deposit.
Even if you eat out everyday you probably won't go over 400 a month, obviously more expensive if you have a girlfriend or whatever.
Nightlife really depends, you could be either drinking from soju bottles outside of convenience stores in hongdae or dropping stacks on bottles in gangnam, but if you find a good group of bros to split bottles with (outside of gangnam) you could get away with maybe 200-300 a month.
Dating more so depends on the girl you're with, there's lots of girls who don't expect anything super crazy, but if they see your lifestyle they might not be too keen on marriage, usually you're going to a cafe, then a restaurant and then somewhere to drink which should come out to around 80-100 per date.
Which visa are you planning on coming on? If you're planning on staying for a significant amount of time you'll need an appropriate visa
