TRS19 Severn Tunnel Project

I'm going to make a route of the Severn Tunnel. I plan to post this to the Download Station when finished. I just need answers to the following:

1. How many baseboards is 198.8 UK km?

2. Should I use SI3D assets?

3. Should I create reskins to go with it?

Please post your answers in the comments.

NOTE: Route may be a large download with over 20 baseboards. Deps will be included.

A baseboard is 720m x 720m.
To my knowledge there is no difference between the "UK km" and the standard "km", so that means:
198.8km = 198.800m
198.800 / 720 = 276,1 so effectively 277 baseboards. For decent scenery / looks you want to add at least one baseboard to each side, maybe more for those nice longer distance looks, so that makes it about 800 baseboards at a bare minimum.
Good luck with that. I hope you have at least a year or two (but likely more) to build that if you aim for decent quality.

Note that the tunnel itself is 7km long.

I don't see why you would want to use fake trains (SI3D) in a real environment. Next to that, they won't let you publish the assets once you have made them anyway, so the "to go with it" part is out of the question. Or at least not legally.
I also consider the reskinning a different project which alone could take a few weeks if not more if you haven't done it before.

Dependencies are normally not included with the download. Most of them are likely to be built-in or on the DLS anyway.
20 baseboards is not a large download (but the estimated 800 is though).

Hope that answers your questions.

If I were you, I would reduce the project to a much smaller route. You can always extend it when done. Many (most?) large route project have failed / never seen the light of day.

Thank you for your input. To address your first answer, I have decided to reduce the length to keep it at a smaller and easier project. I'm not doing this to be lazy, but a 277 - 800 baseboard route would be pretty unethical, if I do say so myself. It will remain very long, yes, but it will not just be tunnel. I hope to add an extra 5 baseboards at either end for extra scenery. This project will be a large improvement from my old industrial branch line put on the DLS years ago. I will be uploading screenshots soon. Stay tuned!