You can always run 2 batteries with an isolator but why? It sounds like you were thinking it would let you run more stuff / draw more current...... not true. HO alt is what you need for that.
The 2nd battery will hide the problem of blinking lights and that but it will never solve it. but there are still advantages of having the 2nd battery. i.e. you can listen to the system with the engine off, as long as you have a split charge relay
mine wasn't too hard to wire up. i put it in between the battery and the amp, put an Earth on it and a remote lead from my stereo as it had a spare plug for a second one.
to be honest with you i'm not too sure if it was a split charge relay or not, its what the guy in the shop told me and he knew his stuff so i took his word for it.
Got rid of it shortly after though as i realised (from this forum) i needed a new alt and that splitting the batteries could mean that i would try to start my car one day and the front battery would be drained
"is it possible to run 2 batts with a stock cadillac alt? if so how do i go about hooking them up?
In the future, my system is going to be pretty extravigant with the neon lights, dual amps, ect.
Eventually, i'll have a HO alt, but for now, will it work?"
All positive together and all negatives together. Wire the batteries in parallel. This will help you with the engine off as you'll have an increased battery bank which is helpful if your batteries are charged to a certain voltage and have a good amount of capacity. If you plan on running all of those accessories with the engine off you should get a high output alternator.