As an over thirty year resident of Southeast Alaska and one who has taken the ferry with a vehicle many times, I don't think you will have trouble with the ferry ramps .... not sure about any sharp turns. I must admit I have not taken my trailer on any ferry trips ... yet.
You can look up the tide levels ahead of time and avoid arrival and departure times on a minus tide.... say a minus 2' or 3' tide. The ferry schedules usually list ferry departure times. To figure loading times, typically subtract about an hour. You can get a free tide app. for your cell phone that will cover anyplace in the US. Southeast tides can vary up to 22' between high and low at extremes. They don't do this every day ... but can at times.
Sometimes in Bellingham you will need to back onto the ferry as the ferry loads from the stern.... but the ferry system has very experienced deck hands and they give you both the time and enough space to turn around and back on. Other SouthEast Alaskan ports have the ferry side tie to the dock so you drive off usually from either port or starboard side doors and that is where you might have to make a sharp turn. You won't have any problem with your 5er. Should it be tight, the deck hands will have the other lanes empty first and then you'll have plenty of room. These ferries handle semi trucks and construction machinery much larger than your trailer ... no problem. Most arrival and departures are simply drive on - drive off.
You will have a great time .... its a wonderland up here. Just for an indication of scale.. its a three day and night ride from Bellingham to Juneau with a half dozen stops in between. Its possible to stop in a port, if you have bicycles with you, to get off and ride from (mostly) one end of town to the other in the typical 45 minute - 1 hour layover time and get back on for departure. Ketchikan, Sitka and Juneau are too "long" to do this but other stops are possible as the towns are quite small and relatively compact. Don't for get to bring a camera and binoculars with you.
As for hitch maneuvering mode or tow mode, I'd put your hitch into as short of a configuration as possible at first. While waiting to board, they may want to measure you. You will have plenty of time to observe loading so you can decide whats best for you. Typically, large vehicles (semi's and such) perceived as heavy vehicles will be directed to inside lanes and lighter weight autos will be directed to outside lanes. You can't sleep in your trailer and if you have pets, they have a pet deck call about every 4 hours so you can "walk" your dog. Bring a roll of paper towels and poop bags so you can clean up after your pet.
You will have a great time,
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