I want to run a TOR node using a small ARM device mini server. I already have a good firewall set but feel a bit uncomfortable when giving away my IP address to the open web by opening a port. If I use a VPN service would it help obfuscate my personal IP address? What are the implications if it does not?
This is a bit of a grey area and it will largely depend on the laws in place in your country. In some countries you can be held accountable for the traffic you allow being passed over your tor node. Some countries consider Tor nodes to be carriers, meaning that if you do not actively monitor all traffic, you can't be held accountable for what goes over it (similar to an ISP).
There are cases where Tor node owners were succesfully prosecuted for hosting a Tor node which was abused for accessing illegal content or masking an attack towards the regular internet. This is of course a risk you need to take into account, if you aren't prosecuted the police might still question you up to a point where it is almost harasment. I'm not saying that this is common, but it can happen, especially in countries where there is less police oversight or strong tendency of censorship/internet control.
In most countries there aren't any clear defined rules, and precedents may exist from previous lawsuits, so it is best to consult a lawyer in your case. Just be aware that you can get into trouble for hosting a Tor node, how noble your cause or intent may be. The fact that it is still used a lot for (unfortunately mostly) criminal purposes puts Tor (or any other anonymity service) in a bad daylight.