If your planning on using an internal hard drive, best bet is to wait till the timed recordings bug is fixed before splashing out any money on a TM Nano. As you already own a TM800 you'll be well aware of TM's track record on bug fixes that never appear !
So if your going to end up paying for a reciever, then extra for a Hard Drive cradle kit and timed recordings still dont work it's not the best scenario. I didnt know about the lack of internal fan for cooling, do they provide an add on fan with the hard disk kit ? If not again it's rather crap having no means to compensate for the extra heat generated by a hard disk.
If your not planning to have a hard disk or use the box for recordings then these issues don't affect you . You should be good to go.
But then again if you dont need internal hard disk capibility buy a VU SOLO clone they're about £90 delivered no internal hard disk support but they run all latest images including VIX and BH and theres no reported timer bugs. Lower spec CPU and chipset though. Or you can always drop a DM800SE with A8P SIM for around the same price as a Nano but they have full internal SATA hard disk support as standard, runs all latest images no timer recordings bugs, silent software contrallable fan as standard.