IC will work for trap to get your feet wet. I would look for #8 1/2 or 9 shot, 8 at the largest. If you can find steel #7 trap load, this will likely pattern tighter from your choke.
The problems you will encounter are that most new shooters are anything but lightning quick at acquiring targets. You'll be firing at the target distance where a full choke would definitely be an advantage. You will get "dusted" targets that do not break, you may even get some that fly through your pattern unscathed. The bigger problem is that you will not get proper positive and negative feedback on your hits and misses. You may be breaking targets on the fringe of your wide pattern and think you're "on". You may also be missing some in the pattern where you were on. The best solution would be to make some buddies at the range, and see if one of them has a properly choked model you may be interested in purchasing at some point (mossberg or Rem 870 would be top picks for a budget gun) that you could try out. An even better option would be to find a skeet range. I find skeet more fun, interesting, and better practice for real life hunting shots, but they don't grow skeet ranges everywhere unfortunately. IC is absolutely appropriate for skeet.
For now, go out, shoot, have fun, concentrate on your stance and follow through until finances allow for an interchangeable choke or second fixed Mod barrel. If you get one with tubes, you may never take the Mod out, but it will be more versatile than fixed IC. That said, I do 90% of my hunting with an IC or skeet choke (similar to IC pattern). About the only time I switch in the field is when shooting diver ducks (specialty waterfowl choke) or skittish pheasants (modified). I shoot trap, including 16 yard mostly with full unless the targets are very jumpy due to wind, then I use a mod.