What are your goals with the RT-AC68U? Are you wanting to set up a VPN and connect to it while traveling or is the 750S just to make an access point for your devices while connected to hotel / coffee shop wifi?

For the AC68U (which is the same router I use!) I’d highly recommend using Asuswrt-Merlin firmware on it. This is based on the stock Asus firmware but adds many bug fixes and options. Well supported on the SmallNetBuilder forums.

The AC68U is a bit under powered for OpenVPN if you are looking for high speeds but it does keep up with most hotel wifi’s that I’ve encountered. The kernel used is too old for wireguard so if that is your plan you’ll need to find another option (I’ve got a Odroid-C2 that runs as a wireguard server for me and I no longer use OpenVPN).

Good stuff! I’d be happy to help if you have questions.