You basically get what you pay for, so there isn't any secret formula. Trek is a reputanle brand and is probably as good as any other on the market.
But have a look, and test if possible, bikes as well as Trek, because different models bave different geometries, and another geometry might feel better to you.
Size also is only really judged by testing, but 56 or 58cm seems a good place to start from what we know about your size. In truth there is very little between these two sizes, so it is unlikely it would be a straight "fit"/"not fit" argument. More likely one size will feel a bit more comfortable to you than the other. If two frames do feel absolutely the same, the smaller frame will tend to be a small amount stiffer and lighter.
Often with bikes you'll face a choice etween a better frame or better components. Of course, it depends how averse you are to upgrading the bike after the initial purchase, but be aware that many components can be upgraded later (although it isn't very cost-effective) but upgrading a frame is usually prohibitive.