The hull form of the British 12" gunned dreadnoughts was similar from Dreadnought through Hercules. To design a Colossus hull enlarge the Dreadnought cross-sections by whatever percentage the Colossus' beam is wider, then space the many Dreadnought cross-sections from 'AoS: Dreadnought' far enough apart for the longer length. There are so many cross-sections the increase in space between each pair would be a fraction of an inch. I don't recall the difference in draft but you might have to adjust the depth of the frames when the cross-sections are enlarged. If a fiberglass hull is made the deck edges can be pushed out far enougth to make up for the slight difference in beam between Colossus and Hercules. I've been thinking of hull mould projects for when I retire from full-time work next year and considering a Dreadnought/Bellerophon hull. It wouldn't be much of a challenge to make a Colossus hull if there was enough demand for them.
Probably you should stick with the original plan to do a Dreadnought/Bellerophon. More of those were launched. Only 3 of the latter were launched if you include Neptune.
I doubt I can hand craft an exact replica of any ship, and considering we are lobbing steel bb's at our models, most fine detail would be destroyed quickly. If someone built a warship and the front turret was not exactly in the right spot, would there be any serious penalty? From what I see, most folks have to tweek the models anyway to squeeze in all the batteries, motors, electronics, guns...etc...etc. As someone very new to the hobby, from my perspective it looks pretty fun, but not exactly like fine scale model work.
Build a ship that you can build correctly. For your first ship if you are already questioning placement, I would strongly encourage you to look at another ship. No one is claiming to have an exact replica, but we are all supposed to be within 1/8th of scale (so moving a turret would keep you out of any sanctioned battles). Read through the builds (really look at the French aircraft carrier build at the top of the warship build sections), they will teach you how to read from plans and build. By the way, what bike did you get?
I think most clubs require the turrets to be in the scale location, within 1/8", but there are some that allow the forward turrets to be raised slightly to facilitate shooting over the bow on ships that had a raised bow (such as the Iowa class BB). Of course, none of these ships are really intended to be display quality, although some are absolutely beautiful (Curt's ships come to mind, there are others)....
