Other people have already said a lot of useful stuff (although I would discourage you from using Volanta in lieu of actual charts because Volanta is often simply wrong with the taxiway names etc.), but I’d like to add a few things 
Re: AIRAC. It sounds like you are using MSFS. In this case, you are in luck, because MSFS regularly updates the AIRAC, so while you might occasionally be 1-2 months behind, you’ll generally be up to date enough for everything to work - most likely the AIRAC you’re using on SimBrief will be the one more out of date. If you still come across a SID/STAR that you don’t have (e.g. FKS1B at EDDF is brand new in the current AIRAC, or you might have a SID that has been updated in the meantime so ATC assigns you ANEKI2L, but you only have ANEKI1L), please inform the controller so they can assign you something different if the procedures are too different from one another. Also, if you don’t want to pay for the Ultimate subscription, Navigraph also has a cheaper (but rather well hidden) navdata-only subscription which will help you keep your sim/aircraft AIRAC up to date as well as the one used by SimBrief.
Re: Charts. As others have said, if Chartfox doesn’t have charts for an airport, chances are high that the AIP (which is where Chartfox gets its charts from) simply requires you to register or that the responsible vACC hosts charts on their own website. However, if you can’t find reasonably up to date charts for an airport at all, you shouldn’t fly at that airport on VATSIM because it’d be near impossible to comply with CoC B8 in this case.
Re: Sceneries. Don’t worry about it too much. People not having sceneries with the latest airport layout is just part of the VATSIM environment, even more so if an airport has recently undergone or is currently undergoing some construction work. Controllers are usually aware of these things and know what inaccuracies default sceneries (or popular addon sceneries) might have - nevertheless, they will work under the assumption that everyone uses an up to date scenery, so you should always inform a controller ahead of time if your scenery is in any way outdated. This way, controllers know what you can work with and find a solution. What I personally always do is look at Little Navmap (which, the way I have it set up, will pull airport data directly from MSFS and displays the taxiways etc.) and compare that to my charts. If I then find an inaccuracy, I will communicate that to the controller as soon as it might become relevant (e.g. in EGLC, I’m missing the parallel taxiway after E, so I tell the controller that I need a backtrack from E when requesting taxi).
As you already said yourself: there is no obligation to pay money to use VATSIM, but in some cases, this will make things harder for you (and potentially the controllers). And while everyone will try to work out a solution, this can only be done by communicating - unfortunately, many pilots don’t communicate and then just end up doing something different than what ATC expected or otherwise cause a bunch of problems. This is the situation that will “piss off” controllers. Nobody will be angry if you communicate what you need/what you can or cannot do, in fact, it will probably make them think “this guy knows what he’s doing” (although depending on ATC workload and what requirements you have, it might take a while until you can be accommodated - take my EGLC example for instance: if there’s a lot of traffic, I might need to wait until there’s room for the backtrack, but if I’m the only person at the airport for the next 2 hours, it’ll be no problem at all).