Is DD-WRT really necessary? There are routers much better than DD-WRT within their same price range because their stock firmware is just really good.How can a router be optimised for 4k video streaming? Are you planning to use it as a media server? I think you've been flooded by marketing.
Theres a lot of important things you didnt mention like
-WAN speeds (basically your upload + download)
- features you're looking for (talking about software such as anti virus, IDS, bandwidth + priority QoS, printer sharing, etc...).
DD-wrt and tomato are firmwares that stick to their particular featureset and design. Once you get used to professional routers you're never really going to want dd-wrt or tomato. Some consumer routers have caught up in features and RMerlin has made really good firmwares for asus routers that have a lot of the features that professional routers have such as configurability (like with openwrt by adding rules).
As for your LAN, are you looking for switched ports or CPU connected ports? In a professional router any port can be WAN or LAN or both, what matters is the block diagram and how well you make use of the architecture. If you're looking for switched ports usually a semi managed switch like
@L&LD suggested would be better than the AC88U's 8 ports because the switch can do more than the AC88U in layer 2 stuff.
you really have to look properly at what your requirements are. Routers have limits determined by hardware and software, they dont have infinite speeds. Things like PPPOE add overhead and slow down the router even more so if your ISP requires using PPPOE to connect that is also significant in choice. If you have gigabit internet and you use dd-wrt or tomato you will be disappointed as the routers they support cant do gigabit due to lack of hardware acceleration for NAT in their firmwares. Hardware acceleration for NAT is closed source in all these routers that they support (especially broadcom) so these firmwares cant implement it.
