Dan you don't normally amend the soil as it can cause drainage problems. Back fill with the same soil that came out of the hole you dug.
There are many fertilizers you can use, the best in my opinion are the slow release fertilizers like Osmocote or Vigoro
http://www.vigoro.com/ProductCategories/PlantFood/PremiumCitrusAvocadoFood/ .
For your red Hibiscus, try the Tropicals section.