On my Coho I beveled only the top of the hull panel and not the bottom of the deck in an attempt to narrow the volume of the gap. It didn't turn out too bad, but one needs to be very careful in the beveling not to cut too far. In the 4mm three ply, you need to be very careful not to cut the outermost ply as it defines the final shape, and the bevel itself needs to be consistant, not wavy. I did end up beveling the deck at the bow and stern to get a very close fit.It all came together very well. I hardly had to exert any pressure to get the hull and deck to line up properly. To make my bevel I finally got myself a small 4 or 5" block plane; it's quick and easy to control. Nothing was needed to fill any gaps where the hull and deck panels did not meet properly on my project, so much as I hate to criticize anyone, I suspect it was the builder's way of doing things that you saw the results of.

I would guess that if you bevel ALL your seams you'll 'shrink' the inside dimensions to the point where the forms will seem too large, i.e., as the forms fit the inside of the panels, and the inside of the panels is what you'd be trimming to a bevel, the dimensions would get out of whack as they would no longer match. And you certainly don't want to get out of whack this early if this is your first time. You could compensate by trimming the forms, but it could get complicated trying to figure out how much.

On all my seams I rounded off the corners by sanding just shy of going through the top ply. It's not quite as hard as it may sound. Often you can start to see the darkness of the plywood glue before you actually penetrate. I did go through in a couple of places, but they're very small; I really don't think anyone will notice them unless I point them out. I think it was worth it to do this; the glass cloth lays better and the final shape seems somewhat 'softer' than it did with hard corners.

Can't help you with tinting the epoxy. I decided to like the contrast, and it's my understanding from 'The Epoxy Manual' you got with the boat kit that any additives will result in a weaker epoxy, whether it's hardwood dust or Cabosil. I could be wrong there. I would also guess that you'd want a 'recipe' with your additives so you would get a consistant tint; certainly in my case the more wood flour I added the darker the result

BTW, if you also got the bulkhead/hatch kit, I'm going to strongly recommend you do as much of that work as you can before you glue the deck to the hull. I'm struggling with that stuff now, and it's a slow pain in the ass. Also, the hatch holes will allow much better access for reinforcing the shear seams at the bow and stern. That instruction manual trick with the 4' stick and plunger didn't go well at all for me, and once I cut the hatch holes I was finally able to scrape up the mess and redo it much better.

If you built kit models as a kid, you may remember that the final result was usually determined by the amount of care and attention and skill invested into it. My older brothers' models were always just a bit better than mine, even when from identical kits. I've been lucky enough to lavish attention on my Coho. I don't think it would be quite as nice if I had tried to do it in the 75 or so hours Pygmy says it can be done in. On the other hand, I do think I could have made an acceptable and decent boat in that time. Depends on what you want and what you have the time, inclination and resources for.

As Paul J. says, I hope this helps.