Cosmic,
Loads of questions but at least I can get you started and point you in the right direction
Design is based on one by a North American guy and works on the principal that water and crud is heavier than oil and will seperate over time. Time is what you need.
When we started and used new oil/SVO I fitted a new fuel filter then checked/cut it open after 5k miles. I could find no crud. So it probably means our fuel system was already very clean and of course then we were using new oil so acid content was low (acts as a detergent and cleans out any muck) or crud content was low. The Terrano has a very large filter built to allow for bad diesel in some areas so doesn't block easily due to it's larger surface area, but we still change it every other oil change - and carry one just in case we need it.
We started with 20/80 and worked up in stages to what we have now. Never had any problems other than the prevailing smell of doughnut shops 8O
The 'Terry' engine lends itself well to veg use primarily due to the IDI engine design and the IP which, like the fuel filter, is built to run with very varied grades of fuel. Bosch copy IP.
We switched to processing WVO due to the increase in SVO prices though we just had a delivery last week of 56l rape oil from Waitrose. They had a one off deal on which worked out at £45 delivered (80p/l)! Otherwise we reprocess. But, yes with SVO prices being high you need to find a lower cost source to make it viable.
If you want to find out more info the best forum to log into and read is this :-
http://www.vegetableoildiesel.co.uk/forum/index.php
One big point to make is don't do this if your vehicle is not in good running order or you want to save £'s by cutting corners. I change our engine oil at 6k. One reason being it is possible for veg to combine with the sump oil and cause polymerisation/gumming = locked engine in a worse case. Not that I have ever seen it but after all frequent oil changes are not expensive if you don't use synthetic.
Cheers,
Paul