The method you use will be dependent on the final style / medium you want.

1. For comics, use the basic method the pros use. At its most basic that is to separate your base colours from the ink line-art that sits on top. In Poser that means two PNG cutout renders of the same size, that are then combined in Photoshop.

You can then freely filter both in Photoshop, without one layer damaging the other.

The very quick example above uses an unpromising dark and grungy figure, with texture completely un-optimised for comics. The first combo shows the most basic layering of a simple bog-standard render, with a line-art render of the same made with Poser's real-time Comic Book in b&w mode. The line-art goes on top, and the base layer has shadows lifted (since it's too dark and grungy) using Photoshop's native Shadows/Highlights. You can either actually knock out all the white to reveal the layer beneath the line-art, or just set the bending mode do that.

The second combo on the right is the same but after filtering the base layer. The lineart layer has also been filtered, with a G'Mic custom preset. The original base layer is then dropped back on top, and set to a Photoshop blending mode. Often this mode can be "Colour", to force the colours back to their pre-filtering original shades (filters often shift colours). But here I've gone for a more stylised look. This is not the finished product, but a good semi-neutral base which can form part of a comic and on which you can build. You might stroke a mask to add a thick 'holding line' around the character, to help them stand out against a dark background.

Forget all about Photoshop Actions. Photoshop plugin filters such as Mediachance's products and G'MIC are your friends there, and are all you need - and one of them is free.

Remember comics require consistency, and that comics buyers will not accept anything that looks like 'Poser art' (ComiXology explicitly bans it from the store). So you need to develop a workflow that gives you that and hides the Poser-ness. But first, learn to make a clean line-art render from Poser, either with Firefly lines-only, or Comic Book. Or both, since both have things that the other lacks.

2. Sketch is really another thread, but know that Sketch can be run on Poser's Comic Book line-art...

The disadvantage with Sketch is that you don't get the render as a .PNG cutout. Which makes it more awkward to use in the Photoshop layer stack.

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Learn the Secrets of Poser 11 and Line-art Filters.