First off, we always need to see pictures of a new boat. Congratulations by the way.
Really need to see pictures of the oil pan, to make an educated guess. There are really a lot of different pans available.
It is possible, that the bolt, that you are referring to, in the dipstick tube, is actually the dipstick itself. Gently remove it and see if the dipstick is integrated into that bolt.
I can't remember the number for the oil filter, but it is just a standard Chevy filter. There are two different filters, a long and a short. Just choose the one that will fit. If the long one will fit, I would do that.
After you change the oil in the boat the first time, you will probably see the value of having a remote mounted filter. If you do end up pulling the engine, i would recommend welding in a 1/2 NPT bung for the hose you mentioned. I would locate the bung at the lowest right rear corner of pan possible.
468 cubic inches is a .060 overbored 454.
You can add oil through the breathers. I like to pull the valve covers, if you have a solid cam, so you can check everything over, including lash.