Hello
I'm pretty new to Malifaux so I'll leave the gaming details to others.
1. You only need to rule book to play as each box comes with the rules for the models on cards.
2. I'd suggest checking out the terrain forum that has a thread of useful resources - http://wyrd-games.net/community/topic/104611-terrain-resource-list/
3. Pass
4. For assembling models Dgraz has put together a really useful overview http://wyrd-games.net/community/topic/104001-a-beginners-guide-to-plastic-modeling/
For painting, I use either Citadel or Vallejo paints but it might be best to see what is available in your local hobby store. As a starting point for brushes you'll want something pretty small (size 1 ish) and I would recommend spending a little more to get a brush that won't fall apart straight away but again the hobby store will be able to offer suggestions.
After that you will want something to mix paint on, I found an old, cracked plate that was destined for the bin that served me well for years as a mixing palette.
I'd also suggest looking into a way to store everything out of the way, unless your wife is happy with a table cluttered with paint pots and modelling equipment. When I started out I found a cheap tool box was an easy way to store everything I needed. I now have a desk set up out of the way so I paint there.
5. The fate decks make things a lot easier so although not essential are recommended.
On top of that you'll want a tape measure, a way to track things like soul stones and various markers and you should be good to go.
Hope this helps and happy gaming