i think the hd750 would be a good match, if you want to be on the safe side. you can set gain on the hd1200 to limit power to around 1000w. honestly, though, difference between what the hd750 puts out vs. 1000w isn't going to be much, you can save yourself some cash and just get the 750. as for fusing, add up your 4ch amp fuse(s) and the recommended fusing for the jl amp. your battery fuse should be somewhere between this value and the capacity limit of the wire you are using.
The HD1200 is an excellent amp for a 12w7. Yes, it outputs more power than what the 12w7 can handle, but if your gains are set correctly, and you refrain from making any major boosts in the response curve, you should have no problem at all.
I used to run a 1000/1v2 on my 10w7, and it easily brought it to distortion with anything over a +3db boost, but with the gain set correctly to the appropriate voltage, and with no boost being used, it was an excellent match, despite outputting about 300 more RMS watts than what the 10w7 is rated at.
As far as the fuse goes, check the owners manual or JLAudio.com. Its probably around 100amps, maybe a little more...