As I arrived quite in the middle of the spring semester (9th of March), I didn't get any introduction day. Though I met my coordinator 2 days after I arrived and she helped me quite a lot. And with the campus map and the city map, it was fairly easy to find my way. And at the beginning of each rotation, I met my supervisor in the hospital hall as to make everything easy!!
I went to the student health centre the day after I arrived, I made an appointment with them prior to departure.

Yes, I got an accomodation through the UAC. It was in Hägersten, 5 km south from the city centre, on the red line of the subway. It is usually not one of the accomodations they offer, but the school of art (Konstfack) that usually offer these rooms for its own exchange students had a couple free in March, so along with a midwife students, I enjoyed this very pleasant 24 m² room, with my own bathroom and kitchen, on a corridor full with students studying art :)
I payed 5000 SKr / month for this room, but it was definitely worth it (new, fully furnished, clean....).
Everything was included in the price and I met a lot of people on my corridor.

I got it only 2 weeks before arriving though (caused some stress but housing in Stockholm is not easy).

Global friends is a good way to make friends there. You will also meet some at the hospital and lots on your corridor.
But I had almost no Swedish friend - only exchange students.

I mainly wanted to discover another atmosphere than the one back home. I think that it is very important to travel when you are young, in order to get a little bit less narrow-minded and definitely more independant, and it's even better to combine studies and travelling as you will be "forced" to immerge yourself in the other country's way of life.
KI has a partnership with my home university, which definitely makes things easier, and the echoes I got from previous exchange students were quite excellent - as well about the quality of the rotations as about the way of life in Sweden (except in winter maybe :) ).
I didn't get very precise information through my home university, I had to make almost everything by myself (they don't have a single person working ONLY on exchange programs, thus they definitely can't be as well organised at KI's coordinators); but as soon as I got in touch with my supervisor at KI, I got very clear answers to all my questions - and most of the time within 10 minutes after I asked them...
How to get a scholarship, an accomodation... were explained quite clearly by both sides.
The vaccines required were the same as those you need as a med student in France, so I didn't make any one more, and I just screened for MRSA prior to departure.

If you have the opportunity... jump on it!

Yes, I took 5 weeks of Swedish lessons, 2,5 hours twice a week. It was good but not enough to get fluent!

definitely a very good environment to study in: not too much stress, no  pressure.
although I definitely think that I work harder under pressure, it was very pleasant to feel so comfortable at the hospital - each supervisor was very keen on teaching, and you were more than welcome to ask lots of questions - while back home you would sometimes feel stupid when asking so many. You don't have much hierarchy in Sweden: even the student gets respect and you don't feel much tension between nurses, doctors etc.
I only took full-time rotations so I can't really compare theory / practice.

Emergency medicine: This rotation has definitely been the best one so far in my medical studies. I have been able to do so much by myself - taking patients alone, doing lots lots of sutures, taking blood samples, setting lines, taking ABG... much more than I did so far. It was quite busy there (4 weeks in Södersjukuset) that I felt a little bit "lost" at the beginning, but I got quite confident after a couple of days.

Surgery:

I spent 4 weeks in Huddinge hospital, on the upper and lower GI sections. I thought I didn't like surgery before, and I "forced" myself to take this rotation - but now I changed my mind as I liked it a lot. My supervisor was very understandable about what we already knew and what we expected - though I had to fight a lot to get very involved when in the operating room; I only made a couple of sutures and stood behind the surgeon most of the time; while back home, senior doctors would be more than happy to leave the OR before the end of the surgery and would let the resident and the student finish it up themselves :)

I spent at least 50% of my days in the OR.

Oto - Rhino - Laryngology:

Same here, thought I wouldn't enjoy the rotation, but I eventually did. I used to find ENT a little bit disgusting but well, I must admit that ir was pretty interesting to combine medicine and surgery in a single specialty. I spent 2 weeks on the throat section, 1 in the nose section, and one in the ear section.

This rotation was in Huddinge again. Quite useful to be able to make a full ENT clinical exam!

Internal medicine: A very good rotation to start with! 4 weeks at Södersjukhuset: 2 weeks cardiology, 2 weeks lung disease.

very friendly supervisors and an excellent atmosphere to learn.

I definitely enjoyed it!