On the 5.3s, behind the oil pressure switch, there is a small filter screen, like a large thimble. If your oil pressure switch has not failed yet, I suggest getting a new one and replacing it and the screen at the same time. The screen might be clean, but you don't know until it's out. If it is dirty, it can wreak havoc on your oiling of the valve train and damage the engine.
My 5.3 uses more oil than I'd like, probably 2- 2.5L/7500km. A bit more when towing. I find it uses oil a bit faster the older the oil gets (might just be perception). I have been using Mobil 1 since I bought it at 98k km and it now has 160k km and the oil usage hasn't changed appreciably. I do echo the comments to keep an eye on that dipstick especially when towing... In fact if I am going to tow for the better part of the day I will overfill the oil just a little bit (1/8L) for a little extra safety.
I tow a TT that I estimate to be pushing 2250kg loaded. It tows fine so long as I am not on a super steep and long incline in which case it will not maintain speed. This only happened once and it was a twisty/steep back road that I will avoid in future. I only tow in drive, not overdrive. Some say it can do it in overdrive. With the 3.42 gears I find the revs are too low and it hunts on anything but downhill unless I have a tailwind. It goes along nicely though at 23-2400rpm down the highway in drive. Yes, the fuel consumption is terrible, 22L/100 ish but after rebuilding the trans once I will do what I can to not do that expensive punch the head again. I do have a quality trans cooler installed and recommend this. My typical summer time trans temps while towing are 175-185F but can reach 200F if on a very long steep incline (rare).
If I recall what I read in the manual, the max tongue load is about 400kg assuming weight distribution bars on the trailer and with zero cargo and zero passengers in the truck other than the 70kg driver. Adjust downward accordingly as you add weight to the truck.
Setting up your tow hitch etc. can be a bit tricky with the auto airbags. I suggest you take time and trial a couple of ways if the hitch head is adjustable in angle and height. If not, dial in the height the best you can. If you adjust the position of the boat to apply at least 10% of the total trailer load as tongue weight, not more than 15%, and still within the noted tongue weight limits you should be perfect once the trailer tongue is set to tow level. Double check the manual to make sure I have noted the correct numbers.
If you require new air bags I recommend the Arnott bags, I have a write up on here somewhere.
Looks like a nice boat.