The chips get broken down to something like coffee grounds with some pieces being a bit larger but still breaking down over time. As for wood species, Wine Caps will break down almost any non-conifer wood. I have a lot of Autumn Olive that grows by a fence line and I cut and chip it every few years. In addition I throw in a fair amount of oak and some hickory as my woods by my house is dominated by those two trees. Further, if you wanted to speed up decomposition (but be prepared for some serious volume reduction—just keep adding in more material) you could add in some whole square straw bales. The straw will colonize faster and break down more quickly than wood chips.
For the first round, I filled my bed with chips, dug fertile holes and backfilled with bagged topsoil (you could use miracle grow mix if you wanted). I grew tomatoes in the fertile holes but feel free to experiment. I have also tried fertile trenches for beans and gotten good results. Wine Caps like to have some soil contact so the fertile holes/trenches help. After the first season, you likely won’t need any more soil as the chips should be broken down.
This is just a starter and if you are still interested I can give more information and point you to some threads that can help.