Kayleigh,
It sounds like you may already understand this, but be careful of a couple of things:
Whatever you apply to the top, apply it to the bottom too. Do not seal the bottom with a varnish if you plan on only oiling the top. This will create an imbalance in the way to wood absorbs moisture from the air. Whatever you do on one side, do to all sides.
I know a couple who used Sapele for their countertops and determined Tung Oil was going to be the right finish for them. I can attest that in appearance they are gorgeous, but it requires a lot of upkeep. They are not "sealed" and there is no film finish protecting the wood from water etc. This leads to rings from glasses and stains from standing water. They spend a lot of time preventing marks like this from happening, which can create stress when you have guests in your home etc. They also have to re-oil every year or so.
I highly recommend you seal the wood with something. epoxy, polyurethane, anything. Anything will be better at protecting the wood than just an oil alone. I would use an oil first, then a seal coat of shellac, then whatever protective layer you want. With the ease of applying poly, and the different sheen's available, you can obtain pretty much any look you want.