Weird. I didn't get the box to post to an existing thread until I started a new one.

BNW is a lot more complicated to play than GNK. If you find Faerun BNW Faerun a bit confusing and you haven't played much civ v then I recommend you try GNK instead of BNW. presumably since it's currently like 20 versions ahead, the GNK version has less oddities in it.

On winning at war.
The AI is stupid. Read up on Civ V tips a bit. You can usually beat the AI with less powerful units if you put your mind to it.
The first thiong you need to consider is whether you really want to fight at all. It's very easy to get negative opinions with all the AI's players and then you can't trade those luxuries you need to keep your people happy.
Keeping your people happy is very important because of the HUGE downsides. Not the least of which is rebels which will spring up and start ravaging all your improvements.

The defender has significant advantage in terms of cities shooting, healing on home ground and potentially on choosing improvements. EG subtle things like forests or less subtle like spell enhancements to stats and glyph of warding.. I think glyph of warding might be a bit of a design bug atm since you don't get it from the spell.
The only thing the attacker has in his favour really is deciding where to attack and when. You can limit the where by choosing where you build. Remember the AI is stupid and it'll pretty much just go for whatever is nearest.
So the best way to fight a war (initially) is to defend.
Towers, castles and walls are all huge plusses and you should plan ahead.
DO NOT move all your units up to your planned victim's border and then say you're only there for a stroll. Because that's a promise you're making and if you break it then it will count against you. If that message pops up say yes and declare war or shelve your plans untill you get the notification your kept your promise.

You want combined arms.
Magicians are very good at blasting cities, clerics heal you and chant, fighters stop enemy uunits killing your magicians and knights offer huge flexibility via their movement as well as being pretty good at hacking things up.
Rotate your units out of combat. You want to keep those experienced units for later so don't just use them up, move them in a rotation round your cleric and out of missile/spell range.