I don't know about the 90, but I've been told that the 225 takes at least 200 hours to fully break in. That is, fully seating the rings and valves. Until they are fully seated, then it would be logical for it to burn a little bit more fuel. When I first got my 225 I made the mistake of babying it too much. When I took it in far warranty maintenance after about 120 hours, the dealer hooked up the HDS which showed that the engine had less than 1 hour at WOT. He told me that at that rate I would never break in the engine, so cut loose to WOT whenever I could for the next 100 hours. The engine has run great ever since. It currently has over 1600 hours.
Yes, definitely change the oil, gear oil, and oil filter. The bottom gear case drain plug will typically have a magnetic bolt. It is not unusual that you will initially see a good bit of metal flakes on the end of that bolt. You will continue to see those metal flakes each time you change the gear oil, but there should be less of them, and more fine particles, every time. Make note or take a picture of what you see there, and clean it off before re-installing so that you will have a good comparative at the next change.
It might also be a good idea to change out the low pressure fuel filter, too. That has likely caught some debris that remained in the fuel line from installation.