My impression is that Trek bikes tend to be rather heavy and stodgy compared to other entry level bikes in the same price range. Trek is the new Schwinn, a solid bike that's widely available and hard to go wrong with, but priced according to brand recognition. With that said, lots of people were happy with Schwinn bikes for decades, and two of my vintage frames are Schwinn. I also ride a 1960's Schwinn cruiser that's on loan from a friend, and I have to admit that it rides quite well.
Higher end Trek bikes? Who knows, not my bailiwick.
A used bike being sold by a shop? You'll pay a premium, but it's probably worth it for knowing that it's probably been checked out before putting on the sales floor.
Vintage bikes? They have some pro's and con's. It helps to know what to look for, or bring a friend along. Bikes with 27 inch wheels will be harder to find good tires for, though the market won't simply evaporate tomorrow. Many older road bikes had limited frame clearance, making it harder to fit wider tires that are preferred for commuting these days. And impossible to fit snow tires if winter riding is in your future.
I ride two vintage frames, but in both cases, I've thrown the bikes together from a hodgepodge of spare parts, and I didn't care that they were mostly trashed when I got them for free or nearly so.
Choice between upright and drop bars is a personal one, and there are no universal rules on which is better for you. I prefer upright, but find straight bars to be painful, so I've equipped all of my bikes with swept bars.
Don't let fear of failure stop you. Make your best guess. It won't be your last bike. In any event, having a spare bike is handy in case your main bike needs repair. My advice to all "new" riders is that your experience as a cyclist will be greatly improved by developing the ability to perform at least basic maintenance yourself. If something breaks on one of my bikes, I order a new part and ride another bike.