I've heard a lot of complicated techniques and combinations for varnishing. But for a relative noob Wargamer, is this a) essential and b) what's the most simple way of getting this done? And does this need to be done before basing the miniature?
It's not really essential. I haven't varnished a model in years. Some people use sprays, sometimes I've heard of people varnishing all their stuff with brush ons (tedious). I stopped varnishing because every now and then I got a bad can that would frost the crap out of my mini. There are ways to fix it, but I found not bothering to varnish in the first place and just taking care of my minis while playing saved more time and money. And there is always the option to use brush ons if its just specific areas you want matted.
you should probably varnish your metal models, because the paint will chip very easily from them. plastic models are fine without varnishing. most good varnishes are shiny when dry, so if you use one of them you should also (afterwards) apply a spray of matte varnish. i have only tested the army painters anti shine, and it works very well, but i hear there are many other brands too. citadel "matte" vanish does NOT work however (at least not the one i have, but that is many years old)
Plastics don't need varnish because they don't chip, I use citadels pot varnish and while its a tad tedious at times you know your getting complete coverage. You can then use either matt varnish sprays or anti shine varnishes from DIY shops to remove the shine. I often use the gloss varnish because it gives a wet look, so if you wish to avoid that use both the gloss and matt varnish to take that edge off. That or just be more carefull with your minis
I've never varnished a miniature before, I just try not to drop them. It really doesn't do much, and after a while (even witgh varnish) your figures will need a few touch ups every now and then.