one thing I wanted to ask was about the generic wash, is Nuln Oil the best one? I mean, if you dont want to go the route of specific colour washes for specific areas for the crappier minis but just want to slap some block areas of colour down and then use a single wash just to give it a bit of definition, hide the mistakes a bit, is there a recommended "default" wash?
Well, there's not an all-purpose one. Nuln Oil is black and it's good for cooler colors and silver metals. But it can darken brighter and warmer colors. Agrax Earthshade is a chestnut color that is better for warmer colors. But they both can have different effects. For example, Agrax on silver makes it look more burnished and grimy.
It depends on what you want, really. But I would say those two washes are the core, and there isn't much you can't do with them. For example, I think Nuln Oil washes blue better than Drakenhof. And on my Death Guatd, I wash the entire figure with Agrax because they are supposed to look grungy.
But I also do that on my Guardsmen too, following it up with more of the base color. I could do Nuln Oil, Reikland Fleshshade, Seraphim Sepia, and Athonian Camoshade- the proscribed color specific washes. But I like that Agrax makes a more exaggerated sense of shading on the face, which makes them look more characterful. And it also gives more definition to the armor and fatigues. And, let's face it, I'm lazy and it's one all over step instead of spot-washing four colors. So maybe there is an argument there for a universal wash?
Color washes are really good at deepening at a color...Druichii Violet on a Leviathan Tyranid's Carapace or Carroburg Crimson on red armor pieces gives it a richer hue. There are some other tricks you can pull with them, like layering them straight onto white primer for cool looking translucent colors- look in the minis painting thread here for my Poxwalkers post.
But really, at this stage, I'd say stick with Nuln Oil and Agrax Earthshade. Experiment and see what works for you.