Fashion photography ins and outs?

So I've been involved with photography for a good 2 to 3 years now and I currently have the following lenses:
-TAMRON AF70-300mm Macro 1:2 Lens
-Nikon 17-30mm standard lens

I also have a few filters for them aswell.

My main question. I'm really interested in fashion photography and it's something I think I'd like to study a little further and really get to grips with and essentially take STUNNING photos. I need a little help though.

- which lens(es) are the best for fashion photography?
- which filter(s), if any, benefit fashion photography?
- can you recommend a decent flashgun? (I have a sunpak one atm, and the amount of time it takes to load between flashes is RIDICULOUS!)

I have a Nikon D40, any other make/model better for fashion specifically?

Any DSLR is fine for fashion photography. The type you lens you might choose varies depending on what type of fashion you are shooting, and the space you have to work with. A 50mm prime is usually a good choice to start with as it will allow full body shots in a reasonably large room, and can also do head and shoulders. For headshots you might want an 85mm prime.

Filters are next to useless for this. Any effects would normally be applied in post-processing.

Flashguns are the most important thing in fashion and portraiture. You'll need at least two off-camera flashes with wireless triggers and some kind of modifier, like softboxes or white umbrellas. If you'll be using a semi-permanent studio space, you could consider mains-powered flashguns rather than battery ones. Mains ones recharge a LOT faster and obviously don't run flat after an hour.

The major hurdle is learning to use flashlight effectively. It's not simple, so I would recommend buying a studio photography textbook and learning the techniques in theory first. Read about key lights, fill lights, reflectors, how to light the background, etc. When you think you can memorise the basics, buy/borrow some extra equipment and have a go. It's hard, but with practice you will improve.