Nataliya Donskaya, DDS

Although a 3D Scan is the ideal way. As mentioned by Dr. Dushyanth, an experienced oral surgeon can determine bone width without it. Getting a 2nd opinion is also recommended. 

That is not necessarily true about the temporary crown being a mold of the old tooth. There is a possibility that your dentist did not have the correct shade for the temporary crown. Keep in mind temporary crowns are prefabricated and permanent are custom made. I'm sure your permanent one will look amazing. 

Excessive preparation may expose regions of tooth dentin, which is the hard tooth tissue under enamel. Resin would help the over prepped tooth but it all depends on how close the dentist got to the root of the tooth.

After root canal therapy, the tooth no longer has a root and is dead. It is recommended to have crowns placed on RCT teeth for extra protection since it loses structure, and also for cosmetic purposes. 

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If you don’t have enough bone, the bone can be rebuilt. It may be possible to have a bone graft placed to create a better structure for a new implant. Do keep in mind that there are other predictors for implant success and failure which are generally divided into patient-related factors (e.g., general patient health status, smoking habits, oral hygiene maintenance, etc).