I'm just looking for some tips to make them healthier, breed faster, etc.Besides the staple diet of dead leaves supplemented with dog/cat food, fruits and veggies, no, they don't really need anything special. Potting soil or coconut fiber works fine as a substrate, and as long as they have lots of decaying hardwood leaves available, most species should breed well for you.
Of course there are exceptions, some rarer species have been entering the hobby lately that have more specific care requirements, but for the majority of the commonly kept isopods, husbandry is rather straightforward.
Question: Could isopods sustain themselves off of just rotted hardwood, or do they absolutely need rotted hardwood leaves?Really just make sure they have a bunch of dead leaves available, and that'll keep them breeding and healthy. Not sure there's anything else you could do to speed up their development.
For reproduction, they pretty much absolutely need rotten leaves. They may produce a few offspring without leaves and can certainly survive without them, but for good, consistent reproduction and decent sized litters, most isopods need rotten leaves.Question: Could isopods sustain themselves off of just rotted hardwood, or do they absolutely need rotted hardwood leaves?