OTA based VCF questions

[Smilen Dimitrov]

Hello list,
we are trying to make an OTA based VCF and so far, the Electronics
Workbench tests have proved to be succesful. However those were done with
some idealisations, so we are in need of some practical guidance. 
1) In the LM13600 data sheet, it is noted that Iabc|max = 2mA. What is the
lower margin for that current, practically? Is it zero, or some value above
that?
2) In our model we used the lowpass VCF cell given in the datasheet, and
connected four in cascade. Given the lower margin and the upper margin of
2mA, is it possible to map them to cutoff frequencies of say, around 50Hz
for the lower margin, and say, around 17 KHz for the upper one? Would some
sort of exp converter be needed to achieve that goal? If so, which one
would be applicable? Where do we locate the schemo for it?
3) In order to drive four VCF cells in cascade, should we use only one
transistor and divide it's collector current to all the cells, or use some
sort of a current mirror? Pros, cons?
4) There was some feedthrough for input signals of amplitude of about
1-10mV, however, when we tested with input signals of greater amplitude, it
was not noticeable. Should we try to eliminate it? If so, how?
5) We would like to make the filter with a knob and a VC input also, and we
are thinking of a resistor voltage divider (I'm not sure if this is the
right term) taken from the power supply, for the knob, and feeding it to an
OpAmp sumer, together with the CV Input at the other input of the sumer
(I'm not sure this is the right term either, maybe it'd be better to call
it mixer ). What we would like is that the both of these inputs be able to
span the entire range of the VCF independently and also when they are
together. When those are pliugged in together, if their sum (or the
eqivalent thereof) goes over 2mA, is the LM in danger of some sort, and
should we make some sort of protection (a limiter or something)?
Well, that should be it for now, sorry for the length, and just one more
note  - we don't really want anything fancy, we just want to keep it simple
and the ckt to work with some degree of efficiency.
Thanks,
smilen & TJ