There can be hundreds of fields on MLS side and sure that there is no such fields in the plugin. But there is no problem to add them. With Fields Builder you can add as many fields and sections as you need.
Please check Fields Builder guide first. Once you add the new fields, they will be all displayed in the drop-down list in Fields Configuration >>
First add new fields via Fields Builder, create new sections first, e.g. Interior Features, Exterior Features, School Information, etc.
Once you add new fields, you will find them in the drop-down list of the plugin in MLS RETS Import >> Fields Configuration >>
You can always get back to Fields Builder and edit any field or section, as well as add any new ones.