I have not been blending long enough to pinpoint all of the pertinent differences, but between the two, I find espresso blending to be a little more difficult. Which is a simple way of saying, "so much to learn..."
Sometimes I use Brazilian as a base, sometimes I don't. I try to match general origin, bean size/moisture content, or both if I preblend; otherwise, I roast each bean separately. Sometimes roasting separately takes too damn long, and sometimes the percentages are so low that its not feasible to do in small amounts.
I think about what each bean will lend to the blend, whether it is a lower toned chocolate, a higher fruited note, or maybe a middle of the road nutty flavor. I think in terms of washed, semi-washed, and dry process when thinking about crema, mouthfeel, and persistency of flavor.
What am I using as my base?
Is this bean X adding or subtracting? In what way?
What degree of roast is optimum for each bean?
Do I use beans with the same approximate optimum roast temperature?
Wait three days.
Test. Test. Test. Change brew temp. Test test test. Change brew temp. Test test test.
Repeat.
Finally come to a conclusion, and either praise or damn the beans.
It's never the roaster's fault... really. *grin*
