Collecting is not a great way to start out in bonsai. It complicates everything. Basic care for a newly collected tree is not the same for an established bonsai. Collected trees require specific kinds of care post-collection that can be difficult for beginners to understand--watering in particular can be a challenge. Soil choices, whether to keep all field soil on the tree, the size of the root mass that is possible or preferable to get all are critical factors in collection.
Even for experienced bonsaiists, Oaks are not the easiest trees to collect. For the most part, They can have deep tap roots and no close feeder roots to work with. Beginner collectors typically have very high rates of loss among the trees they dig. Those rates increase with the age and size of the trees they dig up.
The tree you've pictured is worth collecting, but with no experience, you will most likely kill it. Why not practice on smaller trees for a few years. Kill those, learn from those, THEN move onto better material like this one...