Regarding idea number one:
Since the magic bar will be taking place at Kulturhus (The Culture House), you may consider staying at the hotels that are in the center of the city instead of the hotel nearby the convention center. The magic bar will be at Kulturhus which is right in the center if the city, and nearby the hotels in the middle of the city.
Transporatation to the hotel nearby the convention center by train after 1 am is not good, during the week. The train ride between Central Station and Alvsj is about 9 minutes, with just about a 5 minute walk to the convention center from the train station. The last trains run until 1 am.
If you heed this advice, you'll find yourself saving a lot of money on taxi trips to and from the city in the middle of the night, when you are
closer to your destination in the city, after your visit to the Magic Bar, if you decide to go there. Also the night clubs are also right in the same neighborhood, too.
I myself wil be staying at a hotel in the city a bit further away, but will be able to take the bus
to the train station and then take the train to the convention center. so this will be very easy to do. There are travel passes that cover all the public transportation, as well (except the taxi).