The GL iNet hardware you listed can work, but I think there are better options. Lets start with the remote side. Looks fine. I’m doing about the same thing with the older AR750s, as I have a personal preference to use GL iNet hardware that has been in the field a bit longer and that only uses the OpenWrt network stack, but there are many good reports from users on the MT1300 with current firmware.
On the home side, you have drawn what is known as a double NAT, and you want as few of these as possible. You are already stuck with one double NAT on the remote side. A double NAT means you are translating the IP address twice, once in your ISP router and once more in the B1300 router. Unless you feel that your current ISP router is not properly filtering or not secure, I would keep it as your primary WIFI and Ethernet connection, and add another GL iNet router as either a OpenVPN or Wireguard “VPN appliance”. Future versions of the firmware may officially support serving both protocols on the same GL iNet router at the same time, which can help you work-around VPN issues that you may encounter at different remote sites, as you will then have two different options, on different ports.
The best way to connect this new router working as a “VPN appliance” is to connect it to your Ethernet switch. In your ISP router, you will need to forward the VPN port traffic, and direct traffic for that one port into this new router. Which router to buy depends on the speed you are looking for, so look at the sales literature to help select the product, but remember that for security reasons, you will probably want to turn off WIFI on this device and use it as a dedicated VPN appliance, so WIFI speed is not important. At one place I help manage, I do this with a GL iNet Microuter-N300 as a Wireguard server, but its an older device that I no longer recommend.
The good news is with a bit of work, you should be able to achieve the two goals you stated, as many of us are doing about the same thing.
To have the same external IP address as if I was using it from my home
To be able to access some files that are stored in my home network
Sorry I can’t give you a diagram as I’m on travel and just don’t have the time this morning, but I hope this helps out.