Welcome to OneWorld.
You should try to read and understand the detailed rules here:
http://www.hardlink.com/~markdu/OWFi...eExplorer.html
And then you need to use a OneWorld timetable of some sort - possibly the online one here:
http://www.oneworld.com/schedules/schedules_fr.cfm
to work out which of those cities have OneWorld flights and how to get between them.
You have a fundamental problem in that the basic ticket includes only 4 flight segments in Europe/Middle East. You can purchase 2 more but even with those you will not be able to get to all the places there that you want to go. However, there are plenty of low cost airlines flying around Europe these days, including to many of the cities you list so you should be able to pick up the extra flights quite cheaply.
Remember also that you can only have 20 flight segments in total, and many of the links you list require two or more flights to do: e.g. Seoul - Bangkok would need to be Seoul - Hong Kong - Bangkok.
To answer your specific questions:
1) No - if you buy the ticket in Japan then the Japanese price applies even if the route starts from Seoul. You would need to find either a Travel Agent in Seoul or remotely arrange the ticket with one of the airlines and then pick it up at the airport ticket office.
2) You can only enter each continent once, with only a couple of exceptions. Your routing has a problem in that Delhi is in Asia, so you cannot go there after Australia. You could visit Bangkok after Australia for 23 hours because one of the exceptions is that to get from Australia to Europe you have to pass through Asia, but you can only make a transit (which is defined as a stop of less than 24 hours).
3) See above - outside your continent of origin the number of stopovers isn't restricted. The problem is the limit on the total number of flight segments (20 in toatl, 4 max in each continent except N America where it is 6. You can purchase 2 more per continent except origin (Asia), but you still can't exceed 20 in total).
4) Correct. Since you aren't crossing the Atlantic it doesn't count as an Atlantic Crossing!

But you don't mention New York in your itinerary.
5) Yes - you are travelling through 5 continents: Asia - South West Pacific - Europe/MidEast - South America - North America. Remember that your ticket would need to have the segments necessary to get back to Seoul included in the 20 segment maximum.
At a very quick look the best itinerary I could suggest would be:
ICN-HKG-DEL-HKG-CNS-SYD-BKK(23 hr transit)-LHR-IST-LHR(use separate low cost tickets to get to Venice, Amsterdam, Athens and back to LHR or buy two extra segments on the OWE in the unlikely event it is cheaper)-CAI-BCN-GIG-(either JFK, MIA or SCL)-LAX-HKG-ICN
which leaves you 4 more segments to play with in either North or South America or Australia.
[This message has been edited by christep (edited Dec 25, 2003).]