like… it all depends on what you’re making, you can duplicate some buildings and recolor them but don’t make them like next to each other, add some unique touches to the city, for performance I would say you could use meshparts to reduce the lag (instead of multiple parts merged together) and the coloring really depends on what style your going for, and the lighting gives more life to buildings so that’s another thing you should work on, those are my opinions but it would be good for you to have like a example you’ll look up to, good luck!
EDIT: when making simple builds you don’t need meshes
with building simple things you can just stick with what you got in studio, meshes aren’t as important but instead of like 20 parts, having one mesh with a texture is a bit better (at least from my own experience)
To answer your first question: How do you make a city feel bigger than it actually is?
Make building structures tall, try and vary between smaller buildings too.
Don’t just create one layer of buildings at the end of the city, make a few to make it seem like the city continues in the distance.
Try and keep the city as modern as possible, this should be tall, but thinner buildings.
To answer your second question: How to layout your city to make it look less symmetrical?
Start with the style you would like to implant.
Go onto google images and search for building ideas.
Try to have buildings similar but different, create different shapes, materials, and colours.
To answer your third question: Making a city out of parts affect performance?
Increase lag for players in the game, graphics may need to be decreased.
Rendering delay, mostly when joining the game.
To answer your fourth question: As a builder how do you plan your city’s?
I begin with looking at city examples on the internet, I will then determine what style I would like to introduce into the build. This keeps my builds original, but also adjusted to fit my style.
To answer your fifth question: What color themes do you use in your city builds and why?
It depends, I usually vary them and fit together a few colours so it overall blends, but also is something different and decently looking good.
For modern builds, I try and use light colours or a slightly darker colour that you can find in buildings like modern houses.
For slightly older projects, I generally use darker colours to give that effect to the viewer.
To answer your sixth question: Do bright colors work well in all types of cities?
Like I stated earlier, it depends. If you’re going for an abandoned city or an old fashioned city, for example, you wouldn’t want to be using bright colours.
Something more realistic to this day or something much more future realistic could use bright colours, but try and keep it to a minimum.
I would say it depends on the type of city you are building. Currently I am building a city that is inspired by many midwestern cities, and Las Vegas, so my layout is going to be a grid. In fact most American cities are on a grid layout.
Now, while you’re worried about the city being “symmetrical and blocky” that is sorta the name of the game regarding a city. A great reference in city planning would be the youtube channel City Beautiful, which is a city planning enthusiast who loves to go through and detail city styles. Some suggestions I have to make it feel less “blocky” would be to have roads which are at a different angle, or have a radius. Furthermore, you can use big landmarks such as a highway to break things up too.
As for making the city feel bigger, make the roads narrower, the actual city may be small, but buildings will be closer to each other, creating that city feel.
I also agree with using textures, and that is what I do personally.
As for planning, I like to break my city into sections and build out a few blocks, but also keep in mind generally what will be adjacent to those.
Layout of my city so far, I also included a link if you wanna check it out.