RT-N66U - Vodafone Mobile Wi-Fi R205 integration

Hi,

I got my RT-N66U two days back and I am trying to figure out how to connect it to internet through my Vodafone Mobile Wi-Fi R205. The latter could either be used as a Wi-Fi Access Point or USB dongle. According to the documentation, the USB dongle mode works only on Windows and Mac, i.e. no drivers for linux!

Wi-Fi AP mode supports up to 9 devices and has a range of 10 meters. So my only choice I guess is to use RT-N66U as a wireless client. From what I could test, neither AsusWRT original firmware nor Merlin support repeater mode. I have tried Tomato Shibby but I didn't have success with wireless client mode. I am gonna try Toastman version and see if it supports client mode...

Questions:
Is it possible to use DD-WRT firmware without upgrading CFE to 1.0.1.3? According to its wiki, I could use r18946 or r19342. I found there is even a newer version (r19519) in their FTP site.

Also, could I use Fractal release r20202 (dd-wrt.v24-20202_NEWD_2_K2.6_mini-RT-N66.trx + dd-wrt.v24-20202_NEWD_2_K2.6_mega-RT-N66.trx) without having to upgrade CFE?

Last but not least question :) : If I upgrade CFE to 1.0.1.3 and use Fractal firmware dd-wrt.v24-20363_NEWD_2_K2.6_mega-RT-N66_64K.trx, will I be able to:
1) Flash and use later on AsusWRT Merlin or TomatoUSB Shibby/Toastman without bricking the router?

2) Will I be able to downgrade later on to CFE 1.0.1.2? If so, what is the safe downgrade procedure?

Thanks in advance!