Roughly speaking, Spanish consumismo means the same as English consumerism, and Spanish consumo means the same as English consumption (in the economic sense of "acquiring goods and services").
Spanish consumerismo is a neologism that has nothing to do with English consumerism. According to the Spanish Wikipedia:
El término consumerismo hace referencia a la soberanía del consumidor
respecto a la de la oferta y es utilizado por agentes sociales en
contacto con la defensa de los intereses de consumidores y usuarios,
como las organizaciones de consumidores. Se expresa en los criterios
que usan las personas para adquirir bienes o servicios
El término engloba también un consumo responsable, ético y solidario, > que consiste en consumir con criterios apropiados y racionales…
Summarizing: consumerismo refers to the primacy of the consumer with respect to that of the offer. It is used when speaking of the defense of the interests of consumers and users. It is expressed in the criteria employed by people to acquire goods or services in a conscious manner. It includes responsible, ethical consumption, that is, consuming according to proper, rational criteria.
So in many senses, and in its positive connotations, consumerismo is directly opposed to consumerism, which is a pejorative word.
Note that Spanish also has consunción, which is another word for consumption that refers more to its meaning of debilitating disease (consumption was the old term for tuberculosis in English). Consunción can simply mean "the action and effect of being consumed", but nowadays it's almost never used like that.
ADDENDA: Realizing I didn't answer about one detail... Consumo excesivo is fine (talking about it either as a personal habit, a social custom, or a one-time spree). Just consumismo (for the social aspect) is fine as well. Consumismo excesivo seems redundant, since consumismo by itself already denotes excess. Consumismo sin control/descontrolado/sin freno/desenfrenado etc. come to mind in case you want to emphasize the excess (desenfrenado ~ "unbridled").