what will happen if i delete all my text records before being examined by the customs?

First of all deleting does not completely destroy the files.
You need to use a 'Wiping' program like Eraser.
With this program you can select a bunch of other files that you can put in place of what you just wiped so as to not seem suspicious

They'll probably find you suspicious, but it doesn't seem too troublesome

Why would Customs even look?

They will confiscate equipment and recover everything.