Tony, welcome to wetpixel 
I'm very impressed with the Ikelite housing and the way everything works. I've owned two other Ikelite housings so I'm familiar with their reliability...plus Ike's after sale service is second to none. First dive will be next weekend, so I'll know more then. I have to say that I get aluminum envy when I look at Nexus and Aquatica, but when it comes down to it....I really like being able to see the camera and controls thru the housing....seems silly, but I know where everything is and it's one less thing to worry about........I also bought a rig for my wife's D70 so the cost of two rigs was a major factor in my decision....Now that we've got them set up, I don't regret my decision at all.....after all, it's just a box to keep the camera dry 

Besides the obvious difference between aluminum and polycarbonate, here are a few things to consider:
1. Cost difference is approximately $1000 -$1200 with ports, etc...with Nexus being even a little higher than Aquatica
2. Ikelite mounts the camera to the rear lid of the housing and the others mount the camera on a removable tray in the main housing. The rear mount assures positive contact with the control buttons, but the camera needs to be removed from the tray to change memory cards. Not a major deal to me because I use 4GB microdrives. The removable tray will also let you easily use the camera between dives for topside shots. I haven't experienced changing ports between dives yet...so there may be some other differences between the two setups that I'm not aware of yet.
3. Ports - Aquatica and Nexus have excellent ports that can support different lenses by changing out extension rings, etc. So, one would only buy one dome and/or one flat port and then just get the proper sized extensions for the lenses you have - Ikelite makes a different port for each lens, so you end up with more complete ports to carry around.
4. Aquatica and Ikelite are working on iTTL and that circuitry can be retrofitted in the fairly near future...I prefer manual strobe control unless they design it so that you can switch underwater between iTTL and manual. I would consider that if it happens.
5. Nikon 70-180 micro....Nexus and Aquatica support this lens and Ikelite doesn't...Ike did offer to look at housing the 70-180 if I would send him one to work with...I sold mine before pursueing that option....I'm satisfied with the 60micro and 105micro and a couple of close up lenses
I'm sure others will add to this list. All of these units are excellent and you'll be well served with any one of them. It becomes a personal choice more than "one's better than the other".
I can't help with your strobe and sync cord questions.
Karl