The main question is how much of the "administration" you want to be able to do yourself. You can of course always hire people to do the job for you if you don't have the time or the will, but in the longer run you will always be dependant on someone. The good part is you will always find people here who can help out with certain things.
The next question is if you want to run XenForo only (for now) or do you also have an additional website attached to it (like a Wordpress website or a custom website). This complicates things a lot. If it is only XenForo we are talking about, well, it is very easy to learn, you can do it easily. But managing a main website along XenForo is not that easy.
The last question is if you understand the limitations of the core software of XenForo. As board owners, we all have thousands of wishes we wish we could do with XenForo, but 90% of the time we can't. The core software is limited. I mean it can do a lot of stuff, don't get me wrong, the core features are very robust, good and secure. But we can't do everything we want that easily.
Then there are addons. There are a lot of great addons which extend the functionalities of the core product. With those we can actually do some things we wished we can do. But they are not endless either.
So if you start falling down the rabbit hole where you keep wanting to do things the core can't, then the real problems start. Because now you need bespoken custom development for you. Then you must find developers who can develop it for you, which will be expensive, and with each update of the software or addons, things might break, so you'll need them get fixed. And this cycle goes on and on. Because now you rely on a custom thing only you have, so you are dependent again.
Again, it all depends on how much dependent you want to be. The core product + 3rd party addons can be learned very quickly and easily. You just need to get in, it is not that hard. But if you are like "oh I want this style, and that design, and this customized", well then we are again in custom development territory. Some design stuff one can do oneself with html and css, but that is a bit more advanced than learning the software.
As a start, there is always the manual for XF:
https://xenforo.com/docs/xf2/
Then there are some beginner friendly videos:
https://www.youtube.com/playlist?list=PL71lyEf0D9idDVFxEHykUywlWAxyVDhz8
You always have the commuty here, so feel free to ask anything and search for anything.
Then there is a XF demo you can always use to customize and configure freely anything you want.
I am not sure what your level of knowledge is. You are talking about since 2015, so I am not sure why you would need training. Perhaps you do. Again, without seeing your website it is hard to say. If you need specific things to be explained to you, just ask, we'll try to help. Or if you need the basics explained, I am sure there are plenty of admins who can help out. I can for example, but since I am not an US native, there might be better options than me.
In post nr. 5 you are talking about forms. The core software can't do that but there are 2 addons which can do that. It depends on what exactly you want to do.
Hope it works out for you, feel free to send me a pm if you need any help.
