I am a former DD-WRT user and noticed your firmware for my model (WRT1900ACS v2) of router.
I noticed the layout is completely different and more towards the cisco router side of things. I read through the guide and it seems pretty basic if your not a network tech. Do I also need to know how to use the SSH command line?
No, there is a GUI. The wifi support for that particular model is not great though. Consider it for wired use only.
It is not like Cisco's CLI at all. OpenWrt is a full Linux where you can access and change anything that you want, including modifying any file anywhere (until it is out of flash space). There are a group of config files which trigger scripts that set up everything related to almost all networking tasks. The settings in those files can mostly be accessed with the GUI.
Compared to ddwrt oprnwrt does not come with functional blocks, you can install adblock, printserver, guest portal as separate packages if/when needed. Basic default is nat-ed lan and dhcp wan, youll do some clicks to attach wifi AP to lan. Rest is documented in wiki. Dont be too scared though.
Probably it is added with a grain of salt - whether you need to be expert admin to handle OpenWrt - and the answer is NO, it is simple, but not 1:1 ddwrt interface wise.
Generally, all user land config options will be listed in the documentation. If there is something you need that isn't listed, you can ask. But I would imagine that it is the exception (by far) rather than the rule.