A set of BUIS (back-up iron sights) is always a good idea, even if you do eventually put some sort of glass optic on it. After that, it is entirely dependent upon the role that you envision for the rifle. You say that this will primarily be a plinker - to what ranges? If you'll never shoot past 100 yds, a 0x magnification red dot or holosight may be ideal. If you want more precision, or the ability to reach out much further, then you will want some sort of magnification. No offense at all intended, but the Oracle is an "entry level" AR - it most likely will not be a long-distance tack driver in the accuracy department. Certainly accurate enough for a plinker, however, and with that in mind I think you would be very well served with a Nikon or Leopold 3-9x scope, appropriate offerings from both can be had for around $100. You can go cheaper, but either of these scopes will provide good glass, good durability, and good overall value instead of simply being the least expensive thing you can find.
I love the AR as a plinking rifle for many reasons, one of which is the very versatility that you are discovering. You will likely find yourself changing what you want to do with the rifle a few times, simply because you can...and there's nothing wrong with that! So, in short, my advice is to get a set of quality (not the absolute most expensive, but not bottom of the barrel either) BUIS, and shoot it that way for a while. If you then decide that you want something faster and easier for relatively close-up shooting, look at the red dot type scopes available (there are numerous discussions about them here and on other forums). If you find yourself looking for some magnification, drop a C-note on one of the scopes I mentioned (or similar - there are a few other choices out there in the same "value" category) and try shooting with the magnified optic. If at some point you find that you love the AR and want to step up to one of the upper-tier manufacturers, you'll find a ton of info on doing that on here as well.
Have fun!