It is not possible to have the screen on Apple Watch permanently awake whilst the watch is being worn.
To customise your watch face, follow the instructions here:
Customize the face of your Apple Watch - Apple Support
It is not presently possible to install third-party watch faces or to customise your watch beyond the options that Apple has made available.
If you would like to suggest that Apple considers offering additional personalisation options, you can submit feedback here:www.apple.com/feedback/watc...