At the time of the screenshot, around 1220 days.
Major ones I used for the design of my ship include:
MUS Space Base Furniture (Almost all the beds and a lot of furniture come from here)
Bigger Gravships (Self-explanatory)
Basically, every Vanilla Expanded mod. (VFE Deserters for the 3x3 rocket launchers protecting my noble quarters, VFE: Medieval 2 for the giant purple heraldry in the throne room)
Launch into empty space and Custom Map Generator Size (1st lets you land on empty space tiles, 2nd allows you to modify the space maps to be able to accommodate the modded ship size because the first mod only takes into account vanilla restrictions)
No Gravship Launch Site World Map (No longer leaves a crater everytime you leave a planet side tile)
EGI Holograms and Projectors (All the holographic images)
Cargo Holds - (Massive storage spaces that I used in my garages)
Laser Weapons: Re-Examined (The laser turrets in the middle of my ship)
Automatic Hydroponics (Hydroponics bay)
Floor-Mounted Aquarium (The fishery next to my noble quarters)
ReBuild: Doors and Corners (Gives me some options like glass walls I used for the indoor barns)
ReBuild: Embrasures (Gives me the embrasures that lets my turrets shoot through walls)
Vanilla Vehicles Expanded (My tanks)
AirtightGarageDoors (Lets garage doors be airtight in space)
Gravship Storage (The blue storage boxes in my outer two most garages with the warcasket foundries)
MO Royalty Column (For the columns I used in the noble quarters)
Panels, Frames and Stairs (Stairs I used throughout the ship)
Plus a lot of miscellaneous aesthetic mods here and there like the Wall Heater, Pilot Console Retexture, Trading Console Retexture, Statue of Colonist, etc.
Let me know if you need anything else.
I have a bunch of mods mentioned in the reddit post that lets me modify map size. Basically, the map generates a landing spot around my ship each time, and if I land on a mountain tile the crater just happens to be an exact fit for my ship. https://www.reddit.com/r/RimWorld/comments/1na7xsq/my_imperial_ship_the_house_of_triton_higher_res/
I started off with vanilla size restrictions on my gravship (2000 tiles) - The lower-middle part of the ship used to be the entire original gravship (from the back-console room/lab/workshop all the way up to the duck/goat pens). The original grav engine was located where the current grey altar is. Once I fully completed that portion of the ship, I expanded the Bigger Gravships setting slightly each time (allowing 1-2 more extenders, allowing 500 extra tiles) which allowed me to build the ship organically, wing by wing. It wasn't until I reached the max settings in several aspects of the Bigger Gravships that I concluded the ship was finished at 11,752 tiles.
For me, any ship or multi-room building will always need to have a fully connected hallway system planned out before being built for both aesthetic & efficiency purposes. No room should have their entrance be connected to another room unless it is a sub-room (ex: bathroom) or a public area (ex: library or garage). I must have any two rooms be accessible through one continuous public pathway.
Avoiding square rooms is something I do in all playthroughs, and if I must use a square/rectangular room I try to fill out the entirety of the space. Each room had their wall layout designed before I determined where to place the furniture, so that's why I have so many irregular room shapes and designs as I forced myself to work with those shapes.
I try avoiding repeated floor patterns unless the room is too small. Most of the carpeted rooms have slightly different shades of the same color from their neighbor (turquoise next to aqua, next to light blue, next to sky blue, etc.), but I also made sure to make sure the type of color "matched" its surroundings (the production/manufacturing rooms tend to all be grey/white, the commoners in the middle ship occupy different shades of blue, and nobility at the top with crimson/purple). I tend to try and keep the color/scheme of the furniture-pieces to be similar to their adjacent placement as much as possible. For example, having my medical bays and science labs only keeping to the white/blue/green color scheme and having some adjacent rooms match that scheme (ex: the rooms next to the labs tend to keep the light blue/cream color scheme) whereas my mechanoid production room keeping to a grey/red/blue theme. For the library, I rotated between scroll shelves and book shelves with each row and then switched it up with another type of bookshelf that stored books of a different color scheme. I made sure the public bathroom and kitchens or hydroponics had grated tiles to give the image of a proper drainage system. It's subtle, but without the grated tiles in my hydroponics bays or bathrooms, the rooms actually look a lot worse. Additionally for color, only painting the exterior corners of my ship crimson rather than painting the entire thing made it look a lot better. Generally, for each room type, I try to reference or imagine it to be something I've seen before already in real life.
The 5-panel console is from Vanilla Expanded Props & Decor under the "Imperial" category. It's the only prop on the ship, but I felt that it fit in.