Dynamic routed dual hub-spoke network configuration

So my network has grown a lot over the past couple years and I am unsure how to design my network going forward as in my reading a lot of the documentation says I should change how it works and gives examples that don't really match my network and we've started to see weird routing issues. There is definitely a learning curve going from a mid-size network to a truly enterprise fully redundant network that I am trying to create.

So for the back story about 2.5 years ago my network was a very traditional hub-and-spoke network. I had 14 remote locations all with 2 tunnels to our data center directly because our data center also has 2 separate internet providers. I ran OSPF between the data center and the remote sites with every router and subnet being in the same area and traffic flowed beautifully between everything and life was simple. 15 routers, 28 /30 routing subnets, and 17 /24 networks for devices.

Since then we have grown a lot. By next summer I am going to have 65+ locations as well as a second data center that is a part of a company we purchased. We want to use this new data center as a second hub and would like all of our sites to be actively connected to both data centers with automatic routing and failover.

Documentation on OSPF that I have found states that it is a bad idea to have 50+ routers in a single area. Additionally looking at the math there are going to be 260+ /30 routing subnets, and 70+ /24 networks for devices. This is a lot of growth and it is all happening very quickly so I haven't had time to sit down and make routing changes and create new areas but we have passed 55 sites and we are starting to notice weird routing issues having everything in one area that just miraculously fix themselves when we reboot remote routers which is not my preferred solution. As of right now I haven't set anything up in the new data center or integrated it into our network and am trying to figure out what design changes I should be making.

So I am looking for recommendations or even links to documentation on how to design a network like this and what should be done for routing. Do I need to stop using OSPF, if I continue using OSPF how do I set up the areas with which subnets going into which areas?

TL;DR: Looking for recommendations on configuring dynamic routing on a dual hub-and-spoke network that has two data centers that each have two ISPs.