I'd like to get down to 1 or 2mA for a simple PIC (one of these which have
the interrupt-on-pin-change feature, incl. oscillator), and compromise the
speed as little as possible. Probably someone has studied the possibilities
already, and can give some advice... :-)

I had a look at some spec sheets and some app notes, but couldn't come up
with hard figures as to which type of osc (RC, crystal, resonator) and
which frequency. Obviously it helps to reduce voltage to e.g. 3V, and one
has to go slower than like 4MHz.

Also I'd like to know how the internal RC osc works. In some app notes it
is shown with an external R and C, but I remember having read somewhere
else that it works at around 4MHz with no ext components. ??

Related to this question is how the various io ports are to be interfaced
to 5V when the PIC runs at 3V. I remember having read here that some ports
make it (in a kind of oc configuration) up to 14V; how do I find easily
which ones?

Any help highly appreciated...

(BTW, as you probably can tell, this will be my first PIC design, alias not
my first uC design.)