1.
ARP Tutorial. See
Basic ARP,
ARP Spoofing, and
ARP - Address Resolution Protocol.
2.
Static Entry. A static entry eliminates the need and time spent interrogating the local area network for MAC address corresponding to given IP address. I believe static entries stay in the ARP cache until the system is rebooted. My guess is they are being added to the cache via a "log on" script. Disadvantage to static entry is the time "wasted" troubleshooting when IP address of node it refers to is changed and you're not notified. I'm surprised you have "any" static entries in your ARP cache. I guess it depends upon the network environment you're operating in.
I think a "static" arp entry would only be added for nodes that have a "static" IP address. If the node used dynamic IP addressing, the mapping in the arp table would be invalid as soon as the IP address changed.
I would not expect your host computer's IP address to be in the "arp cache"; certainly not as a dynamic entry. (Although you did show it as computers', so perhaps it is the address of another node on your local area network.)
I'm not prepared to address the "security" issue.
3.
Dynamic Entry. There's a default time to live for the dynamic entries. I don't know what it is or where it is configured. Point being, it's long enough to allow communication with another host or hosts without having to reestablish the mapping for each message; and short enough to remove entries from the arp table for hosts you haven't contacted in awhile. The later is to keep the arp cache to a manageable size and reduce invalid mappings for hosts whose dynamic IP address changed.