235/85 is a nice size for a Defender, it gives you better ground clearance and makes your gearing just that little bit higher without blunting the performance too much, your speedo will under read by about 1 -2 mph as well.
Retread tyres are pretty good these days, if the car is your daily driver then perhaps an all terrain will be a better choice.
The Insa Turbo isn't a bad tyre although wear is accelerated on hotter days due to softer rubber compound.
If your wallet will allow the hit, BFGs will do big mileages but make sure you get locking wheelnuts as they'll attract thieves who know their tyres.
As for steel wheels, the steel modular wheels have a wider offset than standard steels which will increase the track and make your car that bit more stable across the slopes.