you are maxed out with 1 porcupine puffer in a 30g or soon will be.
Also, avoid brine shrimp as it has little nutritional value. Try mysis shrimp instead. Brine is OK for an occassional treat, but is probably better to skip all together. It is the equivalent of feeding twinkies.
The problem with puffers and some of the other aggressives is they are messy eaters. Since their behavior pretty much rules out a clean up crew thus leading to the nitrate issues as mentioned above.
If you cannot get a larger tank in the foreseeable future you might be best off returning the Porcupine and trying a different route for stocking.
Here is a good site for comparing types of fish and their requirements: