Transfer case location - right side of the bike, it's the big black oval shape just under the two oil lines, Look toward the front of it and you will see a big slotted plug. That's where you check the level and fill it. The drain is under the bike, approx under the plug.
Tomba - the grade should be what Yamaha calls for regardless if it's dino, a blend or full synthetic. BTW, most, actually all I know of, synthetic blends, are only required to be 15% synthetic in order to call themselves a blend. In other words, 85% is still straight dino oil. They are pretty much just a waste of money.
You will hear many different opinions on when to switch to synthetic oils, here's mine. I have been using synthetic in my cars, trucks, bikes, and ATVs since 1983. I always go to synthetic at first oil change, right after break in. Or, on used vehicles, as soon as I can after purchase. That means, for the new ones, depending on how lazy I am, it gets changed to synthetic with somewhere between 25 and 100 miles on the clock.m I think my Warrior was getting up close to 50 miles on it when I made the change. In the 26 years I have been doing this I have had nothing other than great running engines.