Yes, the project is possible however, there are some things to consider; Will local codes allow the expansion? You will be replacing a large percentage of the house, about 30% and the cost per square foot could run as much as double the amount of the psf price of the original purchase. Replacing the trusses means the whole roof, shingles, decking, insulation, ceilings and electrical that is in the ceiling. Will the soil have an equal bearing capability under the addition?
Yes, tursses can be used as clear-span; they are typically engineered for that.
It would be far less trying and expensive to continue your search for a house that suits your needs. Unless, of course, the land is that much of a premium location.