Upgrading RAM and storage is obviously trivial. The battery as well, that just requires buying a bigger one for the same model.

As for the screen and trackpad, Lenovo has extensive documentation on their website detailing how to replace components, all the way down to the type of screws you need should you lose some. The compatible parts for any of their model can be found on their website. Although the OEM parts are usually more expensive, you can usually find them online in various shops.

If you go for the aliexpress route, just searching "screen for thinkpad t48" will get you a bunch of screens of varying quality.