TIP: Im not sure if you've made up your mind or not with how you're accomplishing placing models in your levels - But I'd recommend chopping your pieces into small chunks rather than 'whole pieces' (Is what I understood from your post).
The reason for this is so when you get into placing lighting into your city, you wont have to chop things up so much later on, causing you to potentially deconstruct your level..
http://www.conitec.net/beta/aentity-lightrange.htmI hope this is helpful for you, Cheers!
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Any additions to this tip are welcome.