LED's

Lighthouse LED's.  But there are may on this forum that can talk you through circuit designs and LED use.    http://lighthouseleds.com/

Jim, you can Google LED Hobby and find a host of information...The link below is just one of them

Dennis

http://www.modeltrainsoftware.com/ledlights1.html

Evans Designs, a forum sponsor, is where I get all my LEDs. It's the link above and they have many styles, designs, sizes. As far as the how to, I used the advanced search feature on the forum and there are many folks willing to help with lots of examples! Terry

E bay has a lot of led's and Amazon too. 

I agree,Evans Designs,they are great to work with !!!!!!!!!

Jim,

Depending on the style of your streetlights use LED bulbs. Town and Country Hobby carries them and they're cheaper than anyone else. The same for your buildings.

If you're doing a lot of LED's you can save a lot of money by buying the LED's and adding the resistors yourself.

Here's a convenient LED Calculator that will compute series/parallel connections for one or many LED's running from DC power.  It's actually very easy to use LED's, no need to buy canned individual LEDs for many times the price of bare bulbs.

The LED lighting strips linked will run directly off your DC transformer and can be cut in groups of 3. This would be for buildings.

LINK

Here is how I do individual LEDs. You can also use 3mm ones with 2 leads. I usually use warm white. E0Bay is a good source. Get them direct from China,that is where they are made anyway and save$$$

Either of these LEDs, if the resistor is sized for 12 volts would be dimable from your throttle.  You said 12 volts max. Always size resistor for maximum voltage. Since you already have a DC transformer all you need is a resistor. With the strips you don't need one if the max is 12 volts. 

LINK2

Here is a 3mm one used as a headlamp. With the DC transformer you don't need the rectifier or capacitor. 

LINK3

Dale H