How to seth a particle width to Auto for a customized UFO model? And how to call sm-full model of MadGraph?

1)
auto_decays work the same way for UFO models as they do for hard-coded models, e.g. for the SM UFO model:

model = SM (ufo ("../"))
Me = 0
MMU = 0
MTA = 0
seed = 0
error_threshold = 1E-8
auto_decays_multiplicity = 2
?auto_decays_radiative = false
unstable "W+" () { ?auto_decays = true }

2)
This question is ambiguous. MG5 hard-coded models cannot be used in WHIZARD (tho MG1 models could be automatically inside the WHIZARD 1.x series). If you mean whether the UFO SM model can be used the same way as in MG, yes it can. If you mean, are there more general variants than the SM hard-coded model in WHIZARD: yes, there are, e.g. SM_CKM, SM_Higgs, SM_Higgs_CKM, etc. Please consult the manual.

Thanks.