I think you will be alright, a little wider than I like, but I try to take mine everywhere.
Figure the water, the weight of the kitchen, try to center the water over the axle and below the floor, with some type of protection. If you plan to have a spare on the front, consider the battery at the back of the trailer, or just behind the axle. With a torsion axle you do not need as many cross members as it becomes a huge one. I seldom have anything behind the axle, as that is the lowest area, and will drag, 1/8 flat stock is thick enough for skid plates. They do not weigh that much, and the absence of worry makes it worth the weight.
Try to get the 45 degree drop, it will give you the most ground clearance. It does eliminate the parking brake, or at least that is what I have been told, and sometimes they come very handy, but having ground clearance is far more important to me. I can park where I want, I have no control of what I have to get over, through or around. Figure the weight of the trailer and do not go over that number on the axle. Meaning if the trailer is going to weigh 2000 pounds order a 2000 pound axle, it will come with the same brakes, bearing and hubs as the 3500 pound axle. Too much torsion axle is a big mistake, and even some large manufacturers make it.
Draw it out on the floor, figure the weight of each item you intend to put in the trailer.
The center of the spindle on a torsion axle is the line, but remember it will have sag. Figure about 3/4 of inch for that. Meaning it will be farther back when the trailer is setting on it. I normally set 1 inch behind center for every foot of box space. Meaning 10 foot of box, 10 inches behind center. It normally figures out to be pretty close.
Try to keep the front where you can physically lift it off the coupler, even with water in it. Nothing worse than a tongue heavy trailer full of water and having to disconnect and turn it around, re attach.
Take your time on the design, lay it out, think about what will be in the way, what will get hit, where else it could be carried, but as you build, keep lifting the front of it, if it gets to the point where you can not lift it, my personal opinion is that it is too tongue heavy. Mine weigh in as much as 2700 pounds full of water and I can still lift the tongue and hold it with one hand. Go to the back and jump up and down and it will not come off the ground. And can be towed at 100mph. Weight is not your enemy, weight in the wrong place is.
Hope that helps, just think about it and you will figure it out. Not rocket science or brain surgery. Have fun.
