SS 2.4x can prototype be replace fully with jquery yet?
and if so how?

I would like to only load and use jquery js files, but see that prototype is still being loaded. Does the base SS 2.4x still include prototype, or am I seeing things being included by mods?

2.4 still uses prototype for the CMS and form validation. A large part has been rewritten into jQuery but that is currently unstable and won't be released until SS 3.0.

For front end form fields I usually turn off the built in validation and use some other kind - often jQuery.validate.

Have a look at this tutorial for an explantation of how to do it http://ssbits.com/tutorials/2009/using-jquery-for-form-validation/