I'm using vim for python scripting and found that I pretty much often need to jump a word forward
e-button and enter insert mode. Is there some built-in shortcut for this or
ea is reuqired to push all the time?
There's no single-key shortcut for this.
Two keystrokes is already pretty short, but there are a few keys on your keyboard that Vim doesn't already use in normal mode, or that carry out a command already provided by another key, so if you wanted to you could set up your own shortcut with something like:
nnoremap <space> ea
:h normal-index for the complete list of keys that already have functions in normal mode. Anything that's not listed you can use, and anything that has the description "same as ..." would also be a good candidate. See also
:h map-which-keys for some suggestions.