Installing an ERP is a solved problem. ERPnext and Odoo both go in reliably, and the vendor documentation is good. That is not where projects die.
They die at the seams. The shop takes an order but the ERP finds out the next morning. Stock is right in the warehouse and wrong on the website. Finance exports a spreadsheet, edits it, and re-imports it, which means for a few hours a day the accounting truth lives in someone's downloads folder.
Every one of those is an integration that was descoped to make a number look better. And each one quietly recreates the manual work the ERP was bought to remove.
So we scope integrations first and the ERP second. Which systems must agree, how quickly, and what happens when one is unreachable - answer that before choosing modules. A smaller ERP that is genuinely connected beats a larger one bolted alongside the business.
The practical test: after go-live, can anyone in the company still do their job in a spreadsheet? If yes, the integration work is not finished.