I normally do not request things at all. If the mayor likes rose gold and we cannot make any, sure, we request it.
If I am in a place woefully without good metals, I consider myself screwed. I'll ask for bars, sure, but I know the rate at which they will come is clearly not going to cut it. So, we hope for goblins and a good harvest.
In Rimamused, (A huge clear-glass dome of the 0.31.25 era that is still being made,) we are over 15K glass blocks, and not once did I think of asking for wood. Apparently, my consumption is such that the odd-ears routinely bring me 350 cords of wood a go, and it is slightly more each year. (Same with the dorfs and umans.) There are no caverns, so there is no underground tree farm, though upwards is heavily forested, so we CAN cut in the winter if we are bored. (We can easily deplete 350x3 trees before you could hope for a fifth caravan while lamenting that there wont even be a fourth.) [For informational purposes: We are 60+ years old. We used to get about 120? wood way back when. We buy every log, so it seems the others feel like making another 3-6 Urists more every year and bring us the wood. Lots of glass, lots of wood.]
I do buy out all edibles and any libation anyone might have. I tend to buy leather and cloth for a few years or any time I might be low. Sometimes I buy animals for the variety in foodstuffs.
I think currently Rimamused has 350 fools, 28,000 drinks and something like 2,400 meals. Clearly this system is working for us, but YMMV.