I just bought TSW4 standard edition and I am wondering if there are any layers to the 3 new routes from previous dlc ?
Yes. Antelope valley has freight layers which you need cajon pass to activate and then Sherman Hill to get the right ones. The sf f7 also layers in. Ecml has several layers such as the 158, scotsman, 700 and rhtt. There are also ai only nonplayable layers which you need sos, ntp, glossop, wsr, gwe and sehs. If you own a last gen, you don't get the 158 or 700. There is also a reduced timetable giving you much fewer layers For vorarlberg, you need luzern, hbl+101+hrr, dresden riesa and vectron for playable services. You get ai only services if you own tharandter rampe and niddertalbahn
rennekton#1349 : I'm not sure what is the last gen of sehs, I bought it for TSW3, so is that the last gen ?
Original SEHS is on TSW2. SEHS extended is the TSW3/4 version. Most of these questions about the game and layers are answered in the wiki. https://train-sim-world.fandom.com/wiki/Train_Sim_World_Wiki