Well some might see it as a sign of unkempt, so you might lose point there. More so if you are wearing a tie. Remember, long sleeves is to put a status of "smarter" looking.
They might consider that you are more onto the "buruh" worker side. But thats just a theory.

Best if you keep your sleeves down.

Or, look around at the office to see how is their working environment. If all of them have their sleeves down. You will do best to follow their example. If they are all wearing t-shirt, I dont think it will be much of a problem to have your sleeves folded up

Call after 2 week? Yeah you should But dont sound desperate. Just say how much u like the job but u got another job offer from another company and would prefer to work with them (the company ur calling) and hope can get an answer soon

Would I? Yes I would.

Should I? No I shouldn't considering that they already have all my data. If they see it fit me,they will either offer me or etc. But the best would be to just call the interviewer up and thank their time for interviewing you. SAy that you saw another position open. Wonder if you would be suitable to apply for it. This will save u lots of times and headache.