I would start by scraping the soil away from the base of the trunk to determine if there is any nebari. I would then set it against a plain background and take a couple of pictures - one that shows the widest basal flare and another that shows the most trunk movement. That will give a much better idea of what the tree really has to offer. The nebari and the trunk take the most time to develop - the branches of maples can generally be grown from nothing since they back bud very well if there are still nodes along the trunk (and sometimes even through fairly thick bark). Sorry to be so blunt, but a picture like the one you posted (and many others have posted) is really not very useful in giving much feedback on styling.
We can create just about any style of bonsai from just about any material. However, if we start with what the tree naturally gives us we will most likely end up with a much better bonsai and it will take far less time to develop. Going back to your question about chopping the trunk at 1/3 height it depends upon what you are trying produce. If you want a thick trunked, masculine tree then growing it wild and cutting back to new leader that is allowed to grow for a couple of years and repeating can work very well and you will have a bonsai in 10 years or so. If you want a more graceful, feminine tree then you use the lines that are available including some cut back to create a more interesting line and branching and have a bonsai in 3-5 years. I have maples in both styles, most of which need more work. I have been creating more in the graceful, feminine style recently since I think that is a better reflection of how they really grow.