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Please consult AISI. You may use STAD PRO and SAP for the purpose

Aoa. You most probably need to use larger sections to improve Kl/r ratio and load carrying capacity of members. As regards modeling of trusses, since you have not mentioned general arrangement of your analysis model, my response is about general aspects of steel structures modeling only. Trusses are also to be modeled similar to frames, after deciding type of truss (fink, pratt etc) to be used. In case you are using 3-d space model with roofing, loads may be applied to roof directly. Alternately, as in case of a 2-d model, loads may also be applied to the top chord joints of the truss, as per the tributory area of the joint.