Sure, there is no problem with using a .0. For example in 10.0.0.0/23 you'd have

10.0.1.0/32

As a perfectly valid IP address.

Also, routing an entire block allows you to use all of the IP's in said block. So there are ways to do it efficiently, but with routing a block that block is not considered on-network and thus doesn't have a broadcast address nor can it use one.

I had this too. I assumed it would be fine - and it mostly was. However, we tracked a weird bug with some of the companies IoT products not being able to open a connection to the .0. Never figured out if this was a dodgy IP stack on the devices, or if it was the particular mobile carrier in that area of the world. My money would be on the latter though.

That works when the subnet is /23 or larger.