I know, I know; they're all unique situations. Just like how every man in Shawshank is innocent.
Background: I've worked at the same company since January 2011. It's a small (currently ~37 employees, was something like 22 when I started) and growing service laboratory. I started out working as a lab tech (the only lab tech; I've since been replaced with two) working 25 hours a week making $12.50/hr. I managed to get bumped up to 30 hours a week that October, and with increases in business got made full-time in May of 2012. By this point I was making $13.25/hr. At my annual review last May, I got an modest raise up to $13.50/hr.
In September, an opportunity presented itself in the IT "department". Up until then, the IT department only had one member. Due to increased workload and the associated "growing pains" of the company, he had too much to do, and needed someone else. So he recommended me to the partners to join IT. Which was awesome. He and I had developed a friendship prior, and he knew I'd be good for the position. He also liked hiring from within for that, because he wanted to be able to trust someone with the access that IT tends to get. I have zero credentials to qualify for this job, just experience of screwing around with computers and programming. He saw that in me, probably thinking of himself when he joined up in 2008, in a similar position in terms of qualifications (he had no college degree and had just worked odd jobs with free coffee). And it's been going great for us. He's become my "fake manager" as he likes to call it, and IT has been able to get a lot more organized.
About a week after transitioning over to IT, my pay was unceremoniously increased to $15/hr (~$31k/yr). Nobody said anything to me; my paystubs just started reflecting the new rate. I was content with that. About a month in, I stumbled upon one of my fake manager's paystubs and naturally did the mental math without even thinking about it, and learned he currently makes $53k.
This significant disparity was actually reassuring to me at the time, seeing that I had a decent potential "path upwards". It also made me start thinking about my next annual review, which will be in May. I get the feeling that it will be rather financially important. It seems like potentially my biggest jump in income yet (I don't expect anything too dramatic of course, as my fake manager is certainly deservedly getting paid far more than me; he knows our systems inside and out and wrote most of them). I also feel like my fake manager will at some point soon become more of a real manager, giving him more too. All this is conjecture based on my vague gut feelings and my feel for "the way things are done around here".
So come my next review, I don't want to screw it up. If I have an opportunity to negotiate, I would like to as much as I can. My main fear is that if I do something stupid, I don't really have any other real options for work. I like this job, I like the people, and want to keep it, and recognize that I need to stick with it another year or two at the absolute minimum if I ever want to claim any real experience in IT for whatever the future brings. So the "ability to walk away" flexibility in negotiating is essentially nonexistent. Which kind of puts me in a pickle about how aggressive I want to be. In my past reviews as a lab tech, I haven't negotiated anything at all. The most negotiating I've ever done in my life was on buying a car.
Any specific advice? I'm clearly overthinking it, but I don't want to leave money on the table, or burn bridges and do something dumb.