I also had a ski-doo for a long time (since 02) until i bought my 09 nytro. Like everyone has said, it will feel alot more tippy at first, it takes a while to get her dialled in the way you like it. it took a few hundred miles before I felt comfortable on it. I bought c&a razors first thing and it made a huge difference, turns a little hard while moving slow but is a huge improvement I thought.
I tightened up my limiter strap one hole which also helped alot, I recommend that as well, two holes might be even better but I thought one hole was enough for me. A trail tank is not a bad idea if you plan on putting on alot of miles...having to worry about running out of gas just takes the fun out of riding in my opinion. Spending the money and never having to "baby" the sled to the pump was the best money I ever spent. I'll let my buddy on his f6 worry about fuel instead.
If your hands get cold easily I would recommend the big dumbo ear hand guards...they really do a good job keeping my hands warm. Or just get rocks "yamaheater" kit and take care of the problem for good.
These are some of the things I did to make the sled more enjoyable for myself... but no matter what you do I think you'll love it. I have totally fallen in love with electric start...