Congrats on your new purchase. We also went from an Outback travel trailer to the Montana High Country 5er.
Suggestions? If have never pulled a 5er before, only bumper pull trailers, you will find some things easier and some things more frustrating. Give yourself time with the new Monte, in a few weeks, it will feel pretty natural. Also, if you can take it to a parking lot, practice backing up as if backing into a campsite. Take cones, or chunks of wood, or something to use as markers until you figure out exactly where that pivot point is. It is different than a bumper pull.
Talking about practice driving, know exactly how much you can "jack knife" the trailer before hitting the cab of the truck. Again ... empty parking lot. Practice and learn the limitations before you even leave the dealer parking lot.
Next advise: Expect things to fall apart, break, and come loose. Not everything has to be fixed by warranty. Much of what will wiggle loose, you can fix yourself. Just use you head and some common sense. The wait time at dealership repair shops to get serviced can be months! (really). Plan on small repairs yourself and save the aggravation. Things will wiggle loose over the first year. Pay attention to detail the first few months of towing.
Be patient and be sensible stocking the new camper. What worked well in your previous camper might not work well in the new one. Start by putting everything from the old trailer into the new one, unless it's something you really want to discard. Then start replacing and customizing after a few trips out.
About customizing? Every camper, every house, has a natural flow. But it takes time to figure out that flow. Before adding hooks and shelves and pulling stuff out, give "it" a trip or two out before making these changes. We did several changes, but those changes didn't start until we'd traveled in it for over 3 months. Then light switches got moved, hooks went up, and little modifications happened. But only after we gave the original, unaltered floor plan a chance. Just don't be too quick to make changes, because a year from now, you may be changing it again.
And best of all, if you can, sleep in it the first night you bring it home, do so. Then again and again and again. Get familiar with everything before hitting the road the first time.
And most of all ... have fun! Don't be overwhelmed. You purchased the camper for enjoyment! When things get kind of hairy (and they will), just remember the old expression... "A bad of camping is always better than a good day at work!"
2019 Montana High Country 375FL
2014 Chevy Silverado Duramax, 6.6L Dually