Can I add multiple IPs on the same range as my current Linode?

Will I be able to add multiple linodes on the same ip range that the current one is on?

When you add another Linode in the same data center, they will automatically be assigned a new ip from a that datacenter, which may or may not be in the same range as the current one. I'd recommend setting up your Linode's with a private IP and having them communicate with each other that way.

Would I have to setup VPN between linodes as i add more?

You could also setup a VPN, but that would not be necessary. If you wanted to deploy Linodes to multiple data centers, than a VPN might be the way to go as private IPs only work for Linodes within the same DC.

Is my IP actually static and will never change unless i break something?

Correct. Your each Linode receives a static IP that will not change with a few caveats. You are able to swap IPs with another Linode, and you are able to Migrate to a new data center, which will change your IP.

Sounds perfect! Exactly what i wanted to know.
No plan to use it between datacenters at this stage.
Just to clarify.

1 Linode will get public ip of 44.58.67.102 and the other will get 99.45.42.65

then i can create private IPs on them both like
192.168.44.4/24
and
192.168.44.5/24

then those 2 will be able to communicate with one another as if they were on my local LAN?

Yep! That's exactly right.

The main difference between this approach and your local LAN is that other Linode's in the datacenter can also see these IPs. We recommend taht you set up firewall rules for your Linode to secure its network traffic. Check out the Private IPs Community Post for a quick example of this using UFW.

And what if another customer is also using the same private ip range as i am? Wouldn't that cause some form of issue between our networks?

It would not matter if i allow or deny said private IP range, if another client is also using the same private IP, they should and would be able to connect to my linodes via the private network?

I would whitelist specific IPs as opposed to ranges. This should means only your IPs from accessing your Linode. While there is more information in this thread, we have restrictions in place that prevent IP spoofing.