easiest soulution: use the usb host port, if you want an internal one and use the host port you will lose USB client but if you are like me and carry a 10/100 USB dongle then you are probelly better off. you might have to unsolder the usb connector, but IMHO thats better as you can then fit a full size USB port for plugging devices in. you might also want to find a 2 port usb hub thats tiny (one for bluetooth one for back ) as you cant run 2 devices off the same wires, you NEED a hub
for space i recomend the dlink DBT-120 due to its size, its the smallest Bluetooth adaptor i have seen thats easy to get.
external anttena connections are a good idea just follow the same teqnique as wifi hackers including cables and you should be fine