New Macbook Air and Photos App with Multiple Macs

The Photos/iPhoto library package, although shareable, is not designed to be edited by multiple computers at once. Also, there are programs that won't work with the integrated photos file picker in Finder if the library is located externally.
I personally thought a similar idea of having an iPhoto library in a NAS, but scrapped it. I believe as long as you can ensure that there won't be more than one computer accessing the library at any given time, it might be okay. Make a duplicate out of it and test it first.

 

I'd suggest that you use your iMac as a network share and let the MBA access it over the network.
Just needs to setup file sharing in the sharing preference panel in system preferences.

 

It's easier said than done. Photos on MacOS put everything into a package, and it is not designed to be accessed from outside the internal drive. I tried putting my library into a NAS, and it breaks some softwares' integration, especially software from the App store. In the sandbox environment, they expect the photo library to be in the internal main drive of the Mac. It is just not the most versatile method of having a photo library to be honest, although iCloud kinda fix it (but obviously it would cost money for larger storage).

 

You can use a VPN to access your home network. Your router should support making a VPN connection, so it is just a matter of either using the VPN part of the network preference panel, or using tunnelblick.
That will get you a secure connection to your home network, and is useful if you are on a public wifi and need to do banking, etc.

 

If it's an ASUS, then you click the VPN icon on the home page of the router, and configure the VPN server with the usernames and passwords you want to use, then save the VPN config file and open that in tunnelblick on your MBA.

You should be able to login to your router on your home network at 192.168.x.1 for the correct network number of (x)
Then it should have an online built-in manual and/or tooltips near the settings, as well as the manual on the manufacturers website. (Which should be a quick google link.)

It is very useful to have if you are travelling and you'd want to watch the BBC iPlayer for example, as you could just login to home network and your connection is effectively from your home.

 

I have used iPhoto Library manager in the past, with good success. In my view it is worth the money. More recently they have updated the manager - https://www.fatcatsoftware.com/powerphotos/

 

Tunnelblick is an App for openvpn VPNs. It is avaiable from https://tunnelblick.net/ and does the main form of VPN supported in Sierra, as the previous type is no longer consider secure.