Yes, i m looking in other forums also but i thought here may be some swedish people who were to sweden in this forum as well :D
Shush, don't look for other forums, PF is all you need! LOL
First of all - Välkommen till Sverige! :)
Born in Polska, raised in Sverige, fell in love with America so there you have my background. I visit Sweden every few years, sometimes more often.
They never really accepted the British pound in Sweden, German Mark in the past was ok but only a few stores would let you do that, nowadays a few stores will let you pay with the €uro, not common at all. If you take a boat to Finland or Estonia (booze cruise! ;) they'll accept everything -> Swedish, Danish, Norwegian Kronor, Estonian Kroon, Euro, and even grains of gold LOL.
In Sweden you gotta use the krona or kronor [pronounced kroner] in plural. If you persist they might accepted your Brittiskt Pund at few places but you'll get a horrendous rate.
I never really stay in hotels when in Sweden as I have family and friends all over the country but in the past I've stayed at the Radisson SAS Stockholm, I have no idea if it was expensive or not (probably) as it was a crew hotel - company pays. Nice hotel for European standards but nothing extraordinary. Asian and Middle Eastern hotels have gotten me spoiled lol.
If you want something really close to the airport I suggest Jumbo Stay Hostel which is litteraly on the opposite end of Arlanda. It's a converted Boeing 747, which I'm very familiar with :) and it has small but cute and practical rooms, showers, etc.
It has a bitter-sweet meaning to me as my exwife and I stayed there one time and we had a blast. It's not "cheap" but I thought it was reasonable, it's been a while though so prices might have changed.
As far as you venturing out of Stockholm, personally I'd advice against it because you only stay there a few days. I'd say soak in the Gamla Stan' atmosphere (Gamla Staden), it's the old section of the city, i think they called it Rynek? in Wrocław, can't remember.
I'd visit the Vasa ship, an amazing experience in itself.
If you go there with a friend, visit the ice-bar, pretty neat.
Actually typing this from the Anchorage airport and I'll be gone for a few days in case you reply so Trevlig Resa (Have a nice trip) and Vi ses igen (see you again).