@stephtara I get that looking into the abyss of seemingly unending configuration options within a Discourse instance can be overwhelming but with options comes opportunities. With that said, I have two reoccurring thoughts as I read your topics and posts.
First
“We shape our tools and they shape us” yes and I think we can agree Facebook no longer shapes in a desirable way. You seem to prefer Discourse but lament the process and ask for less options and/or an easier config process. Although all that would likely be cool to some and desirable by many this is Discourse not Facebook or some other service that is perceived as being easier to use. My tip is just get on with making your Discourse happen. There is plenty of time for the very much welcome and appreciated eloquent critiques of Discourse later, as you build your community.
Second
I agree 
with @jenmck
As a former colleague used to say “Hey Phil, don’t let perfect be the enemy of the good” in an effort to pull me out of the weeds and remind me of the big picture. Stop making it so complicated, keep it simple and just get on with it.
My suggestions for getting on with it:
- Get the reply by mail system working.
- Don’t add a bunch of categories or tags. Add only one public “Welcome” category for everyone coming from any of the FB groups.
- Add three groups one for each FB group.
- Invite your existing FB staff/mods to their respective groups. You are an excellent writing so craft the appropriate welcome messages for each group and the automatically created staff group/category.
- Send the appropriate notices on FB issuing the invites mentioned above. Note: The invites are group specific and some users may get more than one invite if they staff/mod in more than one FB group.
- Handle all of the structure discussions as a Staff group on Discourse.
- Some of your FB staff/mods will not come right away. That is OK just build it and encourage them to come on in as you work to get away from FB. Build it and they will come…or not.
- At some point relative soon after doing the above open invite your FB members using the invite process and another set of well written messages (FB and discourse). Not every FB user will come right away. Continue to nudge… Build it and they will come…or not.
- Just “post something” on you discourse instance.
Regarding your videos and documents:
- If you have not done so already get a YouTube channel going with all the videos. It will be laborious to create topics/posts in discourse for each video but once done you can index organize things very nicely.
- The documents may bet best placed elsewhere for now. There are numerous options. My preference would be serving them from a static website like Hugo.
In pains me, and maybe others, to see you struggle with getting your Discourse community going. You have folks here on Meta that care about your success. You and your staff/mods can always ask for help here.