1- basically you need to make your ship into flt file and a bdm file with the coordinates to predetermined the spawn location, you will need to upload both files to workshop then subscribe it to load the custom spawn ship into your world.
you can check here for reference

however it is broken at the moment after the 0.9 update.


2- It really depends on the ship class.
https://waywardterranfrontier.fandom.com/wiki/Ships#Ship_classes

in exterior view: 1 pixel = 0.5m
you have a small ship which is 6 meters long and 4.4 meters wide,
times 2, you get 12 pixels long and 8.8 pixels wide.
in interior view: 16 pixel = 0.5m,
that's times 16 space in interior,
but you need rooms for modules, such space may be too small.

So, for small ships I recommend 5 pixels = 1 meter

for large ships I recommend 1 pixel = 1 meter

Let's say you want to port a small ship to the game which is 6 meters long and 4.4 meters wide, multiply by 5, so the ship size is 30 pixels long and 22 pixels wide.

Don't forget to leave some space on the edges for adding shield layers.

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3531789988
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3531704255

Thanks. Creating a type 6 at true scale is literally impossible unless you want to operate only on thrusters, and you can't use the travel drive without engines.

I usually leave a 10px buffer around the larger ships for shields.

It's too bad about the BDM, but I did discover how to add ships to the shops. At least being able to buy one would add to natural progression, but it seems simply buying the ship whole doean't add it to your blueprints.