Excel Data Management and Merging (Power Query if possible)

I have a dataset of aid recipients (more than 400,000 records) in Excel, along with 5 separate Excel files containing voter registration data (Daftar Pemilih - around 500K records each file) which include information such as DUN and PDM.

I am looking for assistance to:

Combine the 5 voter files into a single master dataset
Clean and standardize the data (especially Identification Number / IC)
Match (merge) the BKJ recipient data with the voter dataset based on Identification Number
Add additional columns such as DUN and PDM to each BKJ recipient
Set up a simple and efficient system where I can update the BKJ file easily (e.g. replace file and click refresh)

Requirements:

Prefer using Excel Power Query or a simple, maintainable solution
Must be user-friendly (non-technical users should be able to operate it)
Able to handle large datasets (200k – 500k rows)

Deliverables:

Fully working setup
Clean and structured output file
Simple user guide on how to update and refresh data

Timeline: ASAP (preferably within 24 hours)
Budget: Open to reasonable proposals (prefer simple and cost-effective solution)