How long is a piece of string it will take as long as it takes you to install the guide.
Generally the Website gets updated every 2 weeks or so.
It's entirely possible that the guide itself is out of date, Additionally, specific mods may be using an "outdated" version intentionally. If this is the case, it is usually due to a change in the mod, causing a breaking change in our use case.
Because not all mods, or modders for that matter, are created equal. Building Lexys: LOTD SE involves many mods written by a wide array of authors. Some of the mods we use are designed for Skyrim LE and need to be updated to play nicely with SE. Some of the mods have unnecessary, redundant or conflicting edits that need removal. Some of the mods we only use part of, while a different mod picks up the slack. There are numerous reasons that a mod may need adjustment to ensure that your Skyrim experience is stable and consistent.
The guide includes that mod because I want it! Yes, I understand that not everyone is a fan of every mod. Yes, I know that some people won't like the way I choose to do something or a specific mod I decide to include. If you fall into that category, I apologize. I do try to accommodate the majority of my users, but I also know it's impossible to please every player all of the time. When it comes right down to it, this is my guide, so I decide what mods it includes.
There are many reasons the guide doesn't include a particular mod. If I choose not to include a popular mod, it is most often due to a severe conflict with something I find more important, or because it doesn't fit my vision for the guide. It's also entirely possible that I don't know about your favorite mod yet. If you think a mod warrants inclusion, please feel free to let me know, the worst I can say is "no."
There are two significant reasons that I have chosen not to support Skyrim LE. First, many of the mods included in this guide don't have direct equivalents available for LE. Second, I don't play Skyrim LE anymore and don't feel that it is worthwhile to have a second copy of Skyrim installed for no reason other than to make a small minority of users happy.
I generally don't take mod suggestions but you can post it on the discord and if it peaks my interest I might look at it.