Wisconsinjohn, its been a while since I have done much staining, but I think that would turn out great. The tung oil is going to bring out the wood's natural beauty very nicely, but depending on how much grain you want to show, may not be as much as you are hoping. Google "tung oil elm" and it will show you a very subtle almost "nude" look. If you take some mineral spirits on a rag and wipe it on it will give you a preview of how it will turn out. After it dries it will return to the natural unfinished state. If you are looking for anything else I would look into a stain. As for the poly you listed, since it is rated interior/exterior it should work great and I would think it wouldn't leave any glass rings behind. The more thin coats you use, the better the final product will be, both durability and look. You will want to do light sanding with high grit in between each coat and remove dust with a tack cloth. Be prepared for your whole house to stink like paint thinner for a few weeks after this project. Do you have any scraps you can try it out on? And if you get it done and decide you want a little more protection, you could always use some beeswax over the final coat. It will act like a polish, and could be buffed to a high gloss if desired, but would need a small amount reapplied maybe once every/every other year depending on use.
If you have a woodworking store nearby they should be able to point you in the right direction of what to use to get you what you want, and usually are more than helpful on telling you what process to use and some tips. The box stores usually don't have the same expertise, but if you ask enough different people, sometimes you can figure out what should be done. I wouldn't worry about ruining you nice bar top, as if it doesn't turn out quite like you hoped, you can always strip and sand back to the wood.