You "feel" that you can group in 3-4" circle? Either you can, or you can't. No "feeling" about it.
I'm glad that you mentioned practicing from a treestand because this type of shooting (positioning / posture) is different from target shooting on the gound. Good on you for doing the right thing.
There are many treestand companies out there and they will all fit most trees, oak or otherwise, just about the same way. Just like for cars, you'll get "this one is best" arguments from different people. Many people are brand loyal and only theirs will do. Stands vary in features, design and cost so it really depends on what you want in the end. If it's for practice, I'd recommend a ladder stand. A little more difficult to set up, but once done, getting up and down is easier than in a climber and you'll want to practice, A LOT, from a variety of distances.
Other equipment is pretty much a crap shoot. Some folks go in for an afternoon hunt with way more than they need, IMO. I prefer my bow/arrows, a pair of binos and my range finder...which I consider an important piece of gear. Guessing shot distances is tricky at best. A lot of people claim that they can do so accurately, but I call BS.
Not sure where you got your bow/arrows, but if they were not "matched" to each other, I suggest that you have that checked out. Draw length and draw weight need to be matched to arrow weight and spine. Having mis-matched gear can cause problems.
Lastly (unless you ask more questions), practice, practice, practice. When you think you have practiced enough, practice more.
Good luck.