1. You don't seem to be the one in control of this project. So, you are stuck on this path. Or, do you have the political capital and will to fight to get your way? You're seriously going to piss in someone's Wheaties and when you're standing in the shower in the morning, you better have a smile on your face knowing it's worth it.
2. You work for a major HVAC manufacturer. That's the most exciting thing you can do with your life? It would make me want to slit my wrists every day with a spoon.
3. You have to re-do these applications and make the data integrity robust. That means seriously looking at things like where you can get the most benefit for least amount of cost and/or where the data integrity is shit. "Oh, Jim manages our entire Northwest supply chain and inventory using that Excel spreadsheet he keeps on his desktop." I don't care if you use and Oracle product to get there or a cloud-based, super-redundant shade of the color blue. The only thing your boss's boss cares about is whether you a) prevent the company from losing money or b) make the company more money.
4. Speaking about data center room makes you sound like a systems or support person. This is an application and developer thing.
5. I'm not sure I understand where your pain points are. Customer relationship management? Supply chain? Inventory? Quality control? Payroll/HR? Quantify.
6. Do they pay you enough to worry about this? That might seem flippant, but it's very valid.