Well, your post has been here a week and so far no-one has stepped forward to try to assist you, so I might have a go. First off, the disclaimer: I've not used garageband ever, so I may be far off the mark so take my advise with the requisite grains of salt. It has been awhile since I have done any recording or production and then it has been with audacity or reaper and yeah I tried to get my head around Ableton once until confusion set in.
Generally I would record the drum track first and build everything off of that, or a click track just to keep things in time. Add frills fills and gingerbread after the fact in post processing. Doing things on an iPhone seems adventurous to me after all it is a phone not a full blown PC. As a phone they are amazing, but there are limits in resources available for juggling multiple audio tracks and storing them, which may explain your latency issue.
You might try Audacity and see how it works for you, it seems light on resources, it's free, has a shallow learning curve. Have fun!
"what is this quintessence of dust?" - Shakespeare