I don't think they made an 18 series blade, I thought that too for a bit. It goes from the 15 series to the 16, which is new I think. I haven't bent my 15 series yet with the L3400, not that it wouldn't if I hooked something hard while traveling fast. In slow going it simply spins, ice chains and all. You have more HP and a lot more weight, which is why I'd consider the 26 series blades. Adding hydraulics to any blade is a matter of some steel and some welding. I think the cylinder cost me around $100 plus two hoses and some QC ends for them. Say $150 plus some steel for the brackets. One thing I DID learn the hard way is to get the right size cylinder the 1st time, and be sure it's "engineered" right. I'd recommend going no smaller than a 3" bore cylinder, the blade can have a lot of leverage if you hook something solid. When/if you do, it turns the cylinder into a pump and can over-pressurize your hoses. Larger piston = less pressure on the hoses. There ARE crossover relief valves if you want to add them, I didn't get that fancy.
http://www.tractorbynet.com/forums/hydraulics/192127-cylinder-travel-limiter.html
Here's the thread on the re-build phase of my hydraulic angle saga. I got it right the second time around, no problems since. Yes, I AM knocking wood in the background.. if you add the hydraulics yourself, you need to be sure fully retracted = full angle in one direction and fully extended = full angle in the opposite direction. I bent the first cylinder over-extending it. It's easier than it sounds, just takes some thought and measuring. One potential problem is that with the cylinder mount above the blade I don't have power angle with the blade swung around to face backward. Not an issue for me, I don't plow that way anyway.
I don't worry too much about inside storage anymore. Paint is cheaper than buildings, my gear gets touched up in the fall before the snow hits. My harrows, rotary cutter, post hole digger and 2-bottom plow live outdoors. The tractor and logging winch live in a heated garage. I had concerns about the clutch rusting on the winch, plus it's a pig to store safely unless you have a concrete pad to sit it on. I may eventually build a lean-to for the rest of the gear, but after building a house and horse barn in the last 4 years I'm about done driving nails for a while.
Sean