I came from an ancient-style rudimental background, and in college had to learn to play set in about two weeks. Obviously, there was no set in my dormroom, so most of learning independence happened away from the instrument.
I would suggest a two-pronged approach, since just a pad really isn't the same as set, but a set without hands is almost as bad.
Learn rudiments (especially a nice juicy roll) on the pad. Put the pad away some times and play on a pillow to build up your chops. Get your hand technique really loose and proficient. A lot of people with access to a set from the beginning miss this part and have sloppy technique and only minimal control. Get to the point where you can control any sticking pattern with various hand combinations. Check out John Wooton's (Dr. Throwdown's) Rudimental Remedies, which is a really fun way to learn and apply rudiments. Make sure you work through something like Accents and Rebounds, and maybe check out the Wilcoxon solos because they're a fun way to get your hands moving.
For practicing 2+ way coordination, put the pad away and play on your knees. Practice each combination separately (snare/kick, kick/ride, snare/ride... snare/hat/ride, snare/kick/ride... snare/kick/hat/ride) and then put them together. Then, if you already have the hands, you'll find you can fit the rudiments into the backbeat pretty easily once you add the pad back in. You can do the brain work away from the set - a piece of paper on a towel makes a remarkably cheap practice ride cymbal. A box will make a nice kick. The hihat you'll probably have to imagine. Check out some of JoJo Mayer's stuff. I went to a clinic of his once and it was very helpful.
Finally (or maybe initially), practice with a metronome. A lot. Then get one of the ones that has a "light only" setting and play with that. You need to have an intuitive sense of rhythm. A dragging or rushing drummer is a terrible thing.
Make sure you can play the set a bit with no one else around. You'll need to get past nerves of being on a new instrument before it will flow well. For something small to develop beats on, check out a cajon - for 90% of the gigs I play, it's sufficient. Plus you can pack 2 weeks of clothes in one.
18 months is plenty of time to get to know the set and develop the 2+ way independence (really, you can fake a lot of stuff with 2 way to start, though you won't be playing anything "cool"). I'd say to spend the first half focusing 75% on rudiments and hands, then the second half 50-50. Towards the end you're going to need a set to get comfortable and used to keeping a steady tempo with something so loud, but for the beginning you'll be ok without.