Logical next step?

[deep_al]

I dont think youll need a light like the salvo for quite a while, in the great lakes youll have to be using tri-mix to really need a 21w HID, maybe in a quarry it might be nice, but I would put that near the bottom of your wishlist. 

When i was in your shoes w/nitrox and looking at adv. nitrox +deco procedures, I had an atomic m1 and a large steel tank, I choose to buy an al40 and a second m1.  And then a second tank and 3rd M1 when i was getting closer to taking deco procedures. 

youll need a 40 for advanced nitrox and youll need to know how to handle it well, in the mean time its a nice to sling as a pony bottle, its also surprisingly quick to turn a stage reg into a single tank set up.

Considering you already have a set of doubles I would look at at least 1 high performance (din not yoke) reg to set up a doubles rig. Around here your doubles are going to be in deep cold water, so if you want to save money on a reg I would do that on your singles (shallow water) set up.  I personally find doubles more comfortable underwater than a single tank so I wouldn't be surprised if you spend a fair amount of time with them. That extra stability with doubles and lack of true redundancy with an h-valve might be why Ive never been a big fan of a single large cylinder with an h-valve. 

If your serious about looking down the road at a CCR dont be afraid to start collecting stages and stage regs.  I currently have 2 al80's and 2 al40's, each with a stage reg that i feel comfortable with at any depth.  And I would bet that if you asked just about any other CCR diver I am on the short side of equipment. 

good luck with your decisions, if I were you I would rely heavily on my adv. nitrox/deco procedure instructor's advice.  that class is a fair bit more involving than just about any recreational class and if your instructor suggests a certain equipment set up its for a reason.