DD-WRT router suggestion

I'm not familiar with DD-WRT routers and trying to get my feet wet. I have been part of this group for more than 15 years and I enjoy all of you guys, always so polite and willing to help. I know this is not HS but I know I have smartest people here. I hope this thread can help me step by step, from selecting the right router to segregate my network. I'm, trying to segregate my network from others in my family, i.e. QNAP, files and wifi for guess. plus trying to setup openvpn. No need for wireless router since I have a Unifi access point that has been fantastic, easy to troubleshoot since I need to still use the Verizon router.

Thanks for any help.