>1) For the PIC rated to operate on 3-6V, do they work reliablywhen powered
>   from a 3V lithium battery (ie Duracell DL123?)
<snip>

My experience with the 16LC622 is that they cannot reliably be operated from a
3V lithium battery at 4MHZ.  (The data sheet claims that they will work down to
2V at a max clock of 40KHZ., but I needed a minimum clock of 4MZ.)  With a 4MHZ
crystal some parts will not even startup with a fresh lithium battery (3.3V to
3.6 V).  My local FAE stated that the parts are speced at 4MHZ and 3.0 V.  Other
parts, will work fine at 2.4 V with a 4MHZ crystal.  I ended up using two 3V
lithiums in series to get any sort of reliable operation from the 16LC622.
Remember to test at the voltages you expect with a weak battery.  Good Luck.

----- Steve Miller