Congrats! New bikes are always such fun.

Yes, lose the reflectors! I've seen people do headers on the trail because the reflector broke and jammed in various wheel/brake parts. Ugly business.

I would guess from the road bikes you're riding, you will want to take out some spacers rather quickly because you're used to a more aero-road position. You can move the stem up and down by just putting some of the spacers on top of the stem to experiment with bar height. If you find that you can't get hunkered down far enough over the bars when climbing a steep hill (front wheel keeps lifting), swap some spacers to the top of the stem and try the hill again. You've got a very, very upright position on that bike and space to take the bar down without making it an overly aggressive position. Once you like your new position, you can have the steerer tube on the fork cut so that you don't have all the spacers on the top of the stem. BUT,don't do that until you are sure of what you want. You can't uncut the fork. Another solution is to get a stem with less rise.

Have fun! You've entered a whole new world!