New accounting job - massive databases in Excel!

I’ve just started a new job as a Finance Business Partner at a relatively small business. They do A LOT of things the old fashioned way and there’s plenty of opportunities to improve things.

One of my biggest bugbears at the moment is the sizes of some of their files. Old, redundant formulae and ranges in formulae spanning 10000+ rows when they only need 100 for example is making the files huge and slow to open and run.

They use Sage X3 as their accounting software and extract data into Excel via ODBC - I haven’t seen how this is done yet, but it’s as if it’s extracting all data, in all fields, for all time. And to refresh takes a fucking age.

I want to create something new for querying the database to give me only certain fields, from certain nominal codes, filtered by date ranges.

I know I should be looking into creating power pivot and power query files and also looking at reporting using Power BI, but I haven’t looked into that fully yet. (I know I’m falling behind here!)
Where’s the best place to start unpicking this mess?