I don't think Land Pride makes the 18 series anymore. I don't see it listed on their website.
I see what you mean, there's a better than average chance I was mistaken and they didn't make an 18 series blade. They do make an 18 series in their rotary cutters, I thought there would be that level of blade as well.
In that case, the 15 series blade may be a bit light duty for what you have in mind, although mine's doing 90% of what I need it to do with about the same size tractor. Grading a compacted driveway will be a problem unless you can rip it up first with the box blade rippers. I try to do mine first thing in the spring before the ground gets too hard.
Snow removal is what the 15 series does best, although it's up to moving loose material too. Up to about 12 inches of snow is workable, beyond that and it has a tough time handling the volume. I usually punch a hole through deep snow with the FEL, then finish with the blade. Makes a nice finished job. You may want to consider the skid shoes for the blade as well for snow removal, otherwise your gravel will migrate to the ditch until the ground freezes hard. Again, I built mine from scratch, great excuse to get out the metal-working gear and welder.
The hydraulic angle isn't a factory option until you get up to the RBT40 series of blades, the smallest one that has even a factory hydraulic offset option is the RB35.
I added a hydraulic cylinder to mine because I got fed up with getting on and off the tractor every two minutes while snow clearing. A few hours with a welder and some steel and it was done. There's a whole other thread here about that saga, in particular my discovery that my first attempt wasn't going to work so well. It makes good reading, and may save you some of the problems I encountered.
http://www.tractorbynet.com/forums/welding/189597-adding-cylinder-mount-rear-blade.html
and the re-design phase..
http://www.tractorbynet.com/forums/hydraulics/192127-cylinder-travel-limiter.html
I'll be using mine this weekend to move some soil, I'll see if I can get a video of that and the hydraulic angle in action.
My experience with tractors has been that foresight is much less expensive than hindsight, although the process can be time-consuming. If the missus complains about the amount of time you're spending reading these threads, you can quote me on that if you like.
Sean