Concerning model.auto, theu user can define the set of basic structures (exponential, spherical, nugget effect, ...) that should be involved in the global fit.
There is no problem in using several times the same basic structure (say twice a spherical). In fact, internally, these two sphericals will be initialized differently (with different ranges and sills). Then the two basic structures will evolve independently as if they were different in type.
I do not quite understand the second question. Do you mean that you want to specify the maximum number of a given basic structure (say spherical) in the final result. If so, it suffices to enter the name "Spherical"as many times as this maximum. The only possibility is that model_auto will suppress some (or all) of these basic structures (if their sill is considered as negligeable).
I recall that, on the opposite, you can ask not to suppress these negligeable basic structures by specifying the minimum value of the sill beyond which a structure is eliminated: giving a threshold of 0 will cancel the filtering option.