I have some experience, but not a ton. I'll give this a go. :-)
Deciduous = hardwood, yes. Although to be fair, hardwood varies quite a bit in properties based on the tree, as you might expect. As for identification, the bark tells you much. Not sure where you're from but I bet there's people around you that know what types of trees are out there.
I've harvested wood for aquaria before and would just note a few things. First, some wood is not suitable as it rots extremely quickly, carries pathogens, or might actually be poisonous. Basically stick to beech, oak, cherry alder (which grows by streams where I am from).
I've boiled wood for a while in water (several hours) to help clear out pathogens and leech tanins. I've also baked it in an oven at a low temp (200, maybe?) for a half a day or so.
I hope that helps.
"The clearest way into the Universe is through a forest wilderness." -John Muir