If your diffs are scraping, your lift won't directly help - your diff height can only be changed by changing tyres and/or rims. Get a set of steel 16x8 rims and drop some 285/85 muddies on them. Your axle centres will be lifted from 381mm (standard) to 445mm - in other words, the bottom of your diff will rise by 64mm.
However, you can't really fit rubber like that underneath without a lift and some work on the front guards. It might be best to try and combine a 50mm suspension lift with a 50mm body lift to give you clearance. Those tyres will make the engine labour a lot more, so it would be best to limit their use to off-road - besides, they're probably well outside the legal limit for the Navara.
It'll look bloody mean though. Total height change afterwards should be 164mm.
If your bullbar is from ARB, I think they have brush bars that just bolt on. Might be worth talking to them about it. The ARB bar - in my opinion - sets the standard by which other bars have to measure up to.
So, once you've grabbed your lift and bigger tyres and bolted all that steel on you might be looking at some extra power. You can get a No-Limits chip for about $150 or something like that on e-Bay - it's purely an overfueller. Make sure it works on your type of diesel - I'm not sure, they might be for Common Rails only. ChipIt have a solution for yours and it makes way more power than standard - but as you know that's pricey. You don't NEED that power straight off the bat to enjoy off-roading, but it'll be nice to have one day.
My opinion: make the vehicle more capable first, then get the ponies needed.
While you're adding ponies, consider an intercooler if you don't have one. Either an ASE kit for around the $1400-1500 mark or grab an XR6 and stuff that in the front yourself. It won't give you a LOT of extra horsepower, but it will save you an expensive rebuild if the turbo ever lets go.