Upgrading from 18.06 to 19.07.3 on TP-Link 1043ND


I have a TP-Link 1043ND with 18.06.
Now I read in the changelog for 19.07.3, that the architecture has changed (from ar71xx to ath79).

I have set up Wireguard on the Router, which I would like to keep it's settings, if possible.
I also set up a Swap-partition on a USB-stick.
The Router is in it's own NAT.
My primary Router(Which I use only as a Modem) has
My OpenWRT Router

Would upgrading affect any of that?
Should I remove the Swap first and do I need to re-configure the Wireguard-settings afterwards (I would like to avoid that)?
Installed WG Version is 0.0.20181119-1.

I also tried to update packages today, but it does not work:

root@OpenWrt:~# opkg update
Downloading http://downloads.openwrt.org/releases/18.06.1/targets/ar71xx/generic/packages/Packages.gz
*** Failed to download the package list from http://downloads.openwrt.org/releases/18.06.1/targets/ar71xx/generic/packages/Packages.gz
Downloading http://downloads.openwrt.org/releases/18.06.1/packages/mips_24kc/base/Packages.gz
*** Failed to download the package list from http://downloads.openwrt.org/releases/18.06.1/packages/mips_24kc/base/Packages.gz
Downloading http://downloads.openwrt.org/releases/18.06.1/packages/mips_24kc/luci/Packages.gz
*** Failed to download the package list from http://downloads.openwrt.org/releases/18.06.1/packages/mips_24kc/luci/Packages.gz
Downloading http://downloads.openwrt.org/releases/18.06.1/packages/mips_24kc/packages/Packages.gz
*** Failed to download the package list from http://downloads.openwrt.org/releases/18.06.1/packages/mips_24kc/packages/Packages.gz
Downloading http://downloads.openwrt.org/releases/18.06.1/packages/mips_24kc/routing/Packages.gz
*** Failed to download the package list from http://downloads.openwrt.org/releases/18.06.1/packages/mips_24kc/routing/Packages.gz
Downloading http://downloads.openwrt.org/releases/18.06.1/packages/mips_24kc/telephony/Packages.gz
Updated list of available packages in /var/opkg-lists/openwrt_telephony
Downloading http://downloads.openwrt.org/releases/18.06.1/packages/mips_24kc/telephony/Packages.sig
Signature check passed.
Collected errors:
 * opkg_download: Failed to download http://downloads.openwrt.org/releases/18.06.1/targets/ar71xx/generic/packages/Packages.gz, wget returned 4.
 * opkg_download: Check your network settings and connectivity.
 * opkg_download: Failed to download http://downloads.openwrt.org/releases/18.06.1/packages/mips_24kc/base/Packages.gz, wget returned 4.
 * opkg_download: Check your network settings and connectivity.
 * opkg_download: Failed to download http://downloads.openwrt.org/releases/18.06.1/packages/mips_24kc/luci/Packages.gz, wget returned 4.
 * opkg_download: Check your network settings and connectivity.
 * opkg_download: Failed to download http://downloads.openwrt.org/releases/18.06.1/packages/mips_24kc/packages/Packages.gz, wget returned 4.
 * opkg_download: Check your network settings and connectivity.
 * opkg_download: Failed to download http://downloads.openwrt.org/releases/18.06.1/packages/mips_24kc/routing/Packages.gz, wget returned 4.
 * opkg_download: Check your network settings and connectivity.

DNS seems to work, although very slow:

root@OpenWrt:~# ping google.de
PING google.de ( 56 data bytes
64 bytes from seq=0 ttl=119 time=13.119 ms
64 bytes from seq=1 ttl=119 time=222.774 ms
64 bytes from seq=2 ttl=119 time=151.522 ms
64 bytes from seq=3 ttl=119 time=11.908 ms
64 bytes from seq=4 ttl=119 time=13.178 ms
64 bytes from seq=5 ttl=119 time=13.264 ms
64 bytes from seq=6 ttl=119 time=745.826 ms
64 bytes from seq=7 ttl=119 time=797.450 ms
64 bytes from seq=8 ttl=119 time=14.216 ms
64 bytes from seq=9 ttl=119 time=25.735 ms
64 bytes from seq=10 ttl=119 time=149.444 ms
64 bytes from seq=11 ttl=119 time=19.725 ms
64 bytes from seq=12 ttl=119 time=12.882 ms
64 bytes from seq=13 ttl=119 time=86.351 ms
64 bytes from seq=14 ttl=119 time=323.293 ms
64 bytes from seq=15 ttl=119 time=175.114 ms
64 bytes from seq=16 ttl=119 time=294.952 ms
64 bytes from seq=17 ttl=119 time=20.012 ms
64 bytes from seq=18 ttl=119 time=12.078 ms
64 bytes from seq=19 ttl=119 time=123.983 ms
64 bytes from seq=20 ttl=119 time=17.749 ms
64 bytes from seq=21 ttl=119 time=485.082 ms
--- google.de ping statistics ---
22 packets transmitted, 22 packets received, 0% packet loss
round-trip min/avg/max = 11.908/169.529/797.450 ms

On my PC I don't use the Routers DNS-Server (I don't remember why, maybe there was a Problem)

Try resetting to defaults and manually configuring your router. In general, this is the recommended strategy when you upgrade across major releases (maintenance releases are almost always okay to keep settings). More importantly, certain config files are not compatible across the ar71xx > ath79 transition (the network and wireless files in particular). Unless your configuration is particularly complex, it should not take long to recreate your previous setup.

Okay, so the way to go would the to do a Firmware reset and then directly flash the factory file for 19.07.3 or the sysupgrade one?
My Router is my DHCP-Server, so my PC will no longer get an IP, when I reset and reflash it.
What IP is it then defaulting to or what IP do I need to set my PC then to manually to be able to access the Webinterface/SSH?
Because I remeber hte last time I upgraded I could no longer access the Router and it took me some days of fiddling to be able to gain access to it again.

Do you know which files I need to backup for Wireguard, so I can just copy them back onto the new Firmware and it works and I don't need to change anything on my Wireguard Clients?

I was also thinking about buying a VPN-Access (for Example WeVPN).
Is it possible to configure the Router, that all traffic except manually added sites (for example Netflix) will to through the VPN? Or do I need access to a Proxy to be able to do that? But Proxies usually do not support all protocols right?