To echo @VinceAngelo , you'll need to closely examine what is being given to you. For example, if your Excel worksheets have complex formulas that refer to other worksheet cells, you will have your work cut out for you. On the other hand, if they are just straight up text, int, float etc fields, it won't be too bad.
When you mention that 'Authority can export its schema as an excel file' does that include the data or just the field definitions? You might start with Excel to Table and see how that shakes out for you. With respect to your 'lookup lists for particular attributes' that sounds like you might get away with first converting them to a table and use Table to Domain for starters.
It's all do-able, but you'll need to experiment a bit as you go.
That should just about do it....