Installing firmware for R7800

Hi,

I'm about to receive this router:

https://www.amazon.co.uk/gp/product/B01B4X503S/ref=oh_aui_detailpage_o00...

I want to use OpenVPN to configure ExpressVPN and I'll have Raspberry Pi with Pihole installed on it.

Which firmware should I choose if I want to configure the openVPN on my router? Voxel, openwrt or dd-wrt?

If openwrt, is it better to download the community build and flash it? if so, how do I flash it on a brand new router?

Thanks

You're likely going to get a biased answer since you're in the OpenWrt forum but oh well...
You probably want to go with OpenWrt snapshots or a community build, just make sure you have a way to do a recovery in case it doesn't boot for some reason. The rest should be in the wiki