Hey Tayber!
What everyone said so far seems to be the best courses of action.
Just something to note: although I agree Static Meshes are more efficient, I think it really comes down to what you feel comfortable with.
Personally, I like using a mix of BSP and SM within my levels.
BSP is great if you need some quick edits.
Quick story: just yesterday I added a 300 x 300 wall into my level. The wall was (roughly) the exact size of the player. I usually like to make my walls about 1 1/2 the player’s size (it gives a nice feel considering most walls are not the exact size of the average person). Now I wasn’t about to chop my SM in half then re-export and texture it. I merely created a BSP brush of the same size as the wall (to match the texture up) and using a subtractive brush I cut the wall down, create one seamless wall that was 1 1/2 the player’s height. Now, although this my be deemed “in-efficient” it ultimately comes down to you. It reality that was one of the many BSP brushes in my level. I feel like BSP brushes are like anything else, you have to use them in moderation, but don’t feel like you can’t use them at all (unless you don’t want to).
If it were me, I’d be wary of them in the type of level you are making. When making a big city like that, you need efficiency.
See I just like to map in BSP because that’s what I know best (get started with DOOM Builder/ Source Engine which are both primarily BSP based).
Slowly, but surely I’m starting to get into Static Meshes little by little.
Just make sure you feel comfortable with your way of mapping… that’s the most important part.
~ Jason