I have changed the design of the client and ranger boards slightly to reduce manufacturing overhead. The new client and node Ranger boards will be identical, and the client will have a expansion board to perform trilateration on a Teensy3.2 module (as well as an optional Wi-Fi module). The Nodes will also use the same expansion board with only a Wi-Fi module populated to enable standards support. This sort of setup is also more flexible and could enable different applications to be developed (like tracking a client, rather than a client getting its position).

The Ranger board is only 46x54 mm, so it's reasonably small.

Here is a picture of the Ranger board:

Each board will load the same firmware, however a small solder bridge at the back will determine which operating mode it supports (client or node).

Here is the expansion board (with bridges depending on the operational configuration):

The expansion board is designed to be easily modified or upgraded if you decide to change it later on.

The board will fit (optionally top or bottom mounted) like so:

I'm currently researching suitable alternate ceramic antenna designs, so the design might change slightly, but the overall functionality will remain the same.

Edit: Now with an updated antenna design: